To provide a printer which precisely reproduces positional relationship between a photoreceptor unit and an intermediate transfer unit.

In the printer, the central shaft 14a of a photoreceptor follower roll 14 of the photoreceptor unit 3 is situated almost at an intermediate position between the transfer rolls 21a and 21b of the intermediate transfer unit 6. Accordingly, a press contact force F1 applied from the intermediate transfer unit 6 to the photoreceptor unit 3 acts toward the center of the central shaft 14a perpendicularly to the insertion direction W of the photoreceptor unit 3. The units 3 and 6 are fixed by a locking member, which prevents both the units 3 and 6 from being rotated about the central shaft 14a. This firmly fixes the units 3 and 6 without altering the positional relationship between the units 3 and 6.