To provide a belt fixing device which enables life of a member to be prolonged by preventing a deterioration in durability of a belt due to tilt of a bearing by preventing the tilt of the bearing of a bearing member of a supporting roller provided with a roller side siding restricting part due to a siding force of a belt member, and to provided an image forming apparatus provided with the belt fixing device.

The belt fixing device 8 is provided with the fixing belt 80 as a belt member hung across a heating roller 82 and a fixing roller 81 as siding restriction supporting rollers. The belt fixing device 8 is provided with detaching prevention members 90 and 92 preventing the bearing 88 from being detached in the axial direction by being brought into contact with the bearing 88 as the bearing member supporting the end part of a rotational shaft of the heating roller 82, and the detaching prevention members can be brought into contact with the bearing 88 in two positions.