Assist device and endoscope system

1. An assist device which is applied to a treatment instrument, the treatment instrument including an insertion body to be inserted through a channel of an insertion section of an endoscope, the assist device being configured to assist movement of the insertion body relative to the channel, the assist device comprising:

a flexible tube including a passage into which the insertion body of the treatment instrument is inserted, the flexible tube including one end and an other end;

a connector configured to connect the one end of the flexible tube to the channel such that the passage communicates with the channel;

a first retainer configured to attach a side of the other end of the flexible tube to an outer circumference of the insertion section of the endoscope or to an outer circumference of an operation section connected to the insertion section;

a second retainer being movable relative to the first retainer and configured to hold the insertion body of the treatment instrument; and

a connecting member connecting the first retainer and the second retainer to each other,

wherein the second retainer is detachably attached to the insertion body of the treatment instrument in a direction different from a longitudinal direction of the insertion body.

2. The assist device according to claim 1 , wherein the first retainer is attachable to and detachable from the insertion section of the endoscope.

3. The assist device according to claim 1 , wherein the second retainer includes an elastic member.

4. The assist device according to claim 1 , wherein the second retainer is attachable to and detachable from the connecting member, or the connecting member is attachable to and detachable from the first retainer, together with the second retainer.

5. The assist device according to claim 1 , wherein the first retainer is attached near an end of the flexible tube.

6. An endoscope system comprising:

an endoscope including a channel;

an assist device as defined in claim 1 and connected to an end of the channel by the connector; and

a treatment instrument including an insertion body which is configured to insert into the passage of the assist device and the channel of the insertion section of the endoscope and which is held by the second retainer.

7. The endoscope system according to claim 6 , wherein the second retainer is movable closer to or away from the first retainer.

8. The assist device according to claim 1 , wherein the connecting member includes a proximal end and a distal end, and

the second retainer is movable relative to the first retainer within a range defined by a length between the proximal end and the distal end of the connecting member.

9. The assist device according to claim 1 , wherein the second retainer comprises:

an elastically-deformable tubular retainer body; and

a slit which extends throughout the overall length from one end to an other of the retainer body along a longitudinal axis of the retainer body; and

the slit is configured to allow communication between an inside and an outside of the retainer body.

10. The assist device according to claim 1 , wherein the connecting member comprises one of a chain, a cord member, a flexible member, a stretchable member, or a vinyl tie.

11. The assist device according to claim 1 , wherein:

the second retainer includes a slit through which the insertion body is passed, the second retainer retaining the insertion body through the slit; and

the slit has a width substantially equal to an outer diameter of the insertion body or slightly less than the outer diameter of the insertion body.

12. The assist device according to claim 1 , wherein the connecting member is configured to move the second retainer to a position where the second retainer is configured to be held with respect to the first retainer, without reference to whether or not the insertion section is twisted or how the insertion section is twisted.