To provide a process unit having a photoreceptor drum which can be simply handled and easily attached/detached.

A shaft part 314 at one end of a photoreceptor drum 31A is fitted into a hole 4011 of one receiving part 401, to move the photoreceptor drum from the front of an installation space into the installation space 410. The photoreceptor drum 31A is temporarily supported with repulsion of a cleaning blade 351, and positioned in a predetermined position in the installation space 410. A lock member 500 is retracted against a biasing force from a biasing member 600 so as to cause the lock member 500 to support a shaft part 315 at the other end of the photoreceptor drum 31A. The shaft part 315 at the other end of the photoreceptor drum 31A is supported by the lock member 500 with the resilience of the biasing member 600, thereby locking the photoreceptor drum 31A in an installation state.