To provide a rotary body drive device simply formed and manufacturable at low cost, a photo-sensitive member drum used for the rotary body drive device, a process cartridge having the device and the drum, and an image forming device.

A drive shaft 3 comprises a drive transmission member 7 installed slidably in the axial direction of the drive shaft 3 and fittedly installed in a photo-sensitive member 5, a coil spring 9 installed on the drive shaft 3 and energizing the drive transmission member 7 in the direction of the photo-sensitive member 5, a spring pin 10, and an insert hole 15 for inserting the spring pin 10 therein. A locking groove 29 for locking the spring pin 10 projected from the drive shaft 3 is formed in the inner peripheral surface of the drive transmission member 7. The drive transmission member 7 is moved on the drive shaft 3 against the energizing force of the coil spring 9 and the spring pin 10 projected from the insert hole 15 is locked to the locking groove 29.