PURPOSE: To provide a pivotal mechanism for a rotary body, capable of making the increase of torque extremely little and preventing irregularities in rotation, etc., even if the pivotal mechanism is used under a high temperature.

CONSTITUTION: In the pivotal mechanism for the rotary body constituted in such a manner that a metallic cylindrical inside surface and the outside surface of the fitting part of a bearing member made of a high polymer material mutually form a sliding surface and are relatively rotated, plural grooves 18c are provided in the fitting part of the bearing member 18. Moreover, the grooves 18c provided on the bearing member 18 are constituted to obtain a constant helix angle in the axial direction of the rotation of a cylinder and then, an electrophotographic photoreceptor is pivotally supported by the pivotal mechanism, to constitute a process cartridge and further, an image forming device to which the cartridge can be attached.