A process unit for use in an image forming apparatus includes a drum section containing a photosensitive drum and a drum frame for rotatably supporting the drum, and a developing section containing a developing roller and a roller frame for rotatably supporting the roller. The drum frame and roller frame are coupled so that a mutual distance between the outer peripheral surfaces of the drum and roller is set in an adjustable manner. The process unit further includes an inter-axis distance regulation mechanism provided on one of the drum frame and roller frame in a movable manner by which the mechanism is movable between multiple stages, thereby adjusting the mutual distance in the multiple stages. The mechanism includes a rotation type regulation member which has a plurality of contact surface sites whose distances from a rotation center are different in a radial direction with respect to the rotation center.