PURPOSE: To enable the attaching and detaching of a conveyance unit and the approaching and parting of a sepn. belt by one operation, by interlocking a support lever which approaches and parts the sepn. belt to and from a photosensitive drum to the locking member of the conveyance unit.

CONSTITUTION: When a lock piece 71 is drawn from the locking hole 8 of a body by turning a locking lever 70, a tension lever 55 moves downward and the press contact of a sepn. belt 50 with a photosensitive drum 10 is released and the drawing out (turning in an arrow D direction) of the conveyance unit having a front side plate 64 is made possible. In the stage of containing the conveyance unit, the lever 55 is moved downward by the contact of the angle part 72 of the locking lever and the hole 8 by which the belt 50 and the drum 10 are once parted, and upon completion of the locking, both are again brought into press contact with each other. The damage of both is thus prevented.