An image forming device includes a device main body, a process unit which is inserted into and removed from the device main body, and a lock mechanism which fixes a position of the process unit inserted in the device main body. The lock mechanism includes a slide member, an urging member and a receiving part. The slide member is provided on the process unit and is movable in a perpendicular direction with respect to an inserting and removing direction of the process unit. The urging member is provided between the process unit and the slide member and urges the slide member outward in the perpendicular direction. The receiving part is provided at a position in the device main body displaced from a passage where the process unit passes when being inserted and removed. The receiving part makes contact with the slide member urged outward in an inserting direction.