To provide a bearing mounting device having high productivity, capable of mounting a bearing at a predetermined position easily to prevent occurrence of deformation of a rotary shaft and adverse effect on a surface treated layer and reducing weight and size of a device for mounting the bearing, and having the rotary shaft capable of forming image having high quality, reducing electric power consumption and cost, and saving resources to mount the bearing on the rotary shaft and to provide a fixing device provided with the rotary shaft and an image forming device.

This rotary shaft is provided with a shaft part 1 whose both ends are supported and which can rotate, the bearing 2 mounted at both ends of the shaft part 1, a loaded face 1a formed on outer peripheral faces at both ends for loading the shaft part 1 when mounting the bearing 2, and an abutted receive face 1b received by abutting on an end part 1c on one side when press-fitting the bearing 2 into an end part 1b on the other side of the shaft part 1.