To provide an image forming apparatus such that a unit can be mounted at a regular position in an apparatus main body.

The image forming apparatus is equipped with stay members 507 which are fitted in a pair at right and left positions in a device main body and a slide rail 501 which is installed on the stay members 507 and slidably fitted. A lock projection 502 is provided on a flank of the slide rail 501. The lock projection 502 engages a claw part 109 of a lock bracket 101 in Fig. A rack 107 is formed below the lock bracket 101 and engages a driving gear 102 as a driving transmission member. Consequently, when the lock bracket 101 moves into the device main body as the driving gear 102 rotates, the unit fitted to the slide rail 501 also moves to automatically be drawn into the device main body.