An image bearing member unit includes an image bearing member having a supported portion, a supporting member for rotatably supporting the supported portion, a frame for holding the supporting member, and a spacing maintaining portion provided on the frame or the image bearing member. The spacing maintaining portion is disposed outside the supported portion in a radial direction, and is disposed inside a region where the supporting member supports the supported portion. In a state in which the supporting member is not mounted on the frame, the spacing maintaining portion maintains a spacing between the frame and the supported portion in contact with the image bearing member or the frame. In a state in which the supporting member is mounted on the frame, the supporting member is inserted into the spacing between the frame and the supported portion, from outside of the spacing maintaining portion.