Fixing device and image forming apparatus

1. A fixing device comprising:

a solid or hollow cylindrical heating member that heats a recording medium and has at least one recess or projection provided on at least one end of axial ends thereof, on the outer circumference;

a ring-shaped heat insulating member to be fitted to the axial ends of the heating member, the ring-shaped heat insulating member having, an inner circumference which has an inner surface thereon, at least one projection or recess axially formed on the inner surface of the inner circumference to fit into or receive the at least one recess or projection provided on the heating member; and

a bearing that is configured to rotatably support the at least one end of the axial ends of the heating member via the heat insulating member.

2. The fixing device according to claim 1 ,

wherein the heat insulating member has an axially extending cut out portion, and

the at least one projection or recess provided on the heat insulating member extends over the entire circumferences of the heat insulating member.

3. The fixing device according to claim 1 ,

wherein the at least one projection or recess provided on the heat insulating member is positioned axially in the middle of the heat insulating member.

4. The fixing device according to claim 2 ,

wherein the at least one projection or recess provided on the heat insulating member is positioned axially in the middle of the heat insulating member.

5. An image forming apparatus comprising:

a transfer portion that transfers an image to a recording medium; and

the fixing device according to claim 1 that fixes the image transferred by the transfer portion onto the recording medium.

6. An image forming apparatus comprising:

a transfer portion that transfers an image to a recording medium; and

the fixing device according to claim 2 that fixes the image transferred by the transfer portion onto the recording medium.

7. An image forming apparatus comprising:

a transfer portion that transfers an image to a recording medium; and

the fixing device according to claim 3 that fixes the image transferred by the transfer portion onto the recording medium.

8. An image forming apparatus comprising:

a transfer portion that transfers an image to a recording medium; and

the fixing device according to claim 4 that fixes the image transferred by the transfer portion onto the recording medium.

9. The fixing device according to claim 1 , wherein the at least one recess or projection of the solid or hollow cylindrical heating member and the at least one projection or recess of the ring-shaped heat insulating member have an overlap with the bearing in an axial direction of the radius of the solid or hollow cylindrical heating member.

10. A fixing roller comprising:

a solid or hollow cylindrical heating member that heats a recording medium and has at least one recess or projection provided on at least one end of axial ends thereof, on the outer circumference;

a ring-shaped heat insulating member to be fitted to the at least one end of the axial ends of the heating member, the ring-shaped heat insulating member having, an inner circumference which has an inner surface thereon, at least one projection or recess axially formed on the inner surface of the inner circumference to fit into or receive the at least one recess or projection provided on the heating member; and

a bearing that is configured to rotatably support at least one end of the axial ends of the heating member via the heat insulating member.