A process unit includes a photoreceptor drum, a charging roller, and a cam member. The cam member includes a mounting portion that externally fits to a shaft portion of the charging roller and a contact portion that protrudes to an outside of the mounting portion. Then, the charging roller is maintained in a separate state by bringing the contact portion of the cam member into contact with an outer surface of the drum main body, and the charging roller is switched to a contact state by rotating the cam member dependently with rotation of the photoreceptor drum in a normal direction.