Liquid administration device

1. A liquid administration device comprising:

an inner structure that includes:

a cylindrical body comprising:

an inner cylinder that has a bottom part in a distal portion thereof and an opening portion in a proximal portion thereof, the inner cylinder being fillable with a liquid,

an outer cylinder that is concentric with the inner cylinder and extends around an outer periphery of the inner cylinder, the outer cylinder being rotatable relative to the inner cylinder around a central axis of the inner structure,

a needle tube that is mounted in the distal portion of the cylindrical body and has a sharp needle tip at a distal end and a proximal end of which is communicatable with an inside of the cylindrical body, and

a gasket that is located in the cylindrical body and is slidable in an axial direction of the cylindrical body;

an operation member that includes a plunger configured to press the gasket, the operation member being configured to perform a pressing operation in which the plunger is moved relative to the cylindrical body in a distal direction while being pressed;

wherein the plunger comprises:

an elongated plate-shaped part, and

a first engagement portion that comprises at least one stepped portion in which a width of the elongated plate-shaped part changes;

wherein the outer cylinder comprises a second engagement portion;

wherein the first and second engagement portions are configured to enter an engaged state in which the first engagement portion and the second engagement portion are engaged with each other, and the pressing operation is inhibited, and

wherein the first and second engagement portions are configured to enter a released state in which the first engagement portion and the second engagement portion are disengaged, and the pressing operation is performable; and

a rotary portion configured to cause the first engagement portion and the second engagement portion to relatively rotate around a central axis of the of the inner structure and thereby move from the engagement state to the released state.

2. The liquid administration device according to claim 1 , further comprising a rotation inhibiting portion configured to selectively inhibit the relative rotation of the first engagement portion and the second engagement portion around the central axis of the inner structure in the engaged state.

3. The liquid administration device according to claim 1 , wherein the second engagement portion includes at least one protruding portion that protrudes toward the inside of the cylindrical body.

4. The liquid administration device according to claim 3 , wherein the second engagement portion includes a slope located at an end portion of the protruding portion and on which the first engagement portion abuts.

5. The liquid administration device according to claim 4 ,

wherein the outer cylinder is rotatable relative to the operation member around the central axis of the outer cylinder due to the first engagement portion moving relative to the second engagement portion along the slope.

6. The liquid administration device according to claim 1 , further comprising a cover member that is movable between a position (A) at which at least the needle tip of the needle tube is covered and a position (B) at which the needle tip is exposed from the cover member and a liquid is dischargeable through the needle tube due to the cover member being retreated in a proximal direction from the position (A).

7. The liquid administration device according to claim 5 , further comprising a cover member that is movable between a position (A) at which at least the needle tip of the needle tube is covered and a position (B) at which the needle tip is exposed from the cover member and a liquid is dischargeable through the needle tube due to the cover member being retreated in a proximal direction from the position (A).

8. The liquid administration device according to claim 6 , wherein the first and second engagement portions are configured such that the first and second engagement portions enter the engaged state when the cover member is positioned at the position (A) and enter the released state when the engaged state is released by the cover member moving to the position (B).

9. The liquid administration device according to claim 7 , wherein the first and second engagement portions are configured such that the first and second engagement portions enter the engaged state when the cover member is positioned at the position (A) and enter the released state when the engaged state is released by the cover member moving to the position (B).

10. The liquid administration device according to claim 6 ,

wherein the rotary portion includes:

a spur that is provided in one of the cover member and the outer cylinder, and

an inclined first groove that is provided in the other of the cover member and the outer cylinder and into which the spur is insertable, and

wherein the outer cylinder is configured such that the outer cylinder is rotatable relative to the cover member around the central axis by the spur moving relative to the cover member along the first groove such that the outer cylinder is rotated relative to the operation member around the central axis of the outer cylinder.

11. The liquid administration device according to claim 8 ,

wherein the rotary portion includes:

a spur that is provided in one of the cover member and the outer cylinder, and

an inclined first groove that is provided in the other of the cover member and the outer cylinder and into which the spur is inserted, and

wherein the outer cylinder is configured such that the outer cylinder is rotatable relative to the cover member around the central axis by the spur moving relative to the cover member along the first groove such that the outer cylinder is rotated relative to the operation member around the central axis of the outer cylinder.

12. The liquid administration device according to claim 9 ,

wherein the rotary portion includes:

a spur that is provided in one of the cover member and the outer cylinder, and

an inclined first groove that is provided in the other of the cover member and the outer cylinder and into which the spur is inserted, and

wherein the outer cylinder is configured such that the outer cylinder is rotatable relative to the cover member around the central axis by the spur moving relative to the cover member along the first groove such that the outer cylinder is rotated relative to the operation member around the central axis of the outer cylinder.

13. The liquid administration device according to claim 12 , wherein the rotary portion includes a biasing member configured to bias one of the first engagement portion and the second engagement portion to the other of the first engagement portion and the second engagement portion in a rotational direction of the inner structure around the central axis.

14. The liquid administration device according to claim 13 , wherein the biasing member is twisted in an initial state.

15. The liquid administration device according to claim 1 ,

wherein the rotary portion includes a biasing member configured to bias one of the first engagement portion and the second engagement portion to the other of the first engagement portion and the second engagement portion in a rotational direction of the inner structure around the central axis,

wherein the biasing member is twisted in an initial state.

16. The liquid administration device according to claim 6 ,

wherein the rotary portion includes a biasing member configured to bias one of the first engagement portion and the second engagement portion to the other of the first engagement portion and the second engagement portion in a rotational direction of the inner structure around the central axis,

wherein the biasing member is twisted in an initial state.

17. The liquid administration device according to claim 1 ,

wherein the second engagement portion includes a slope on which the first engagement portion abuts, and

wherein the outer cylinder is rotatable relative to the operation member around the central axis of the outer cylinder due to the first engagement portion moving relative to the second engagement portion along the slope.