An image forming device includes, a main casing, a drawer unit, and a transfer unit. The main casing has a first frame formed with a first opening and a second frame formed with a second opening. The main casing has a first inner space in communication with the first opening and the second opening. The drawer unit is movable between a first position and a second position. The drawer unit is accommodated in the first inner space when the drawer unit is in the first position. The drawer unit is partially drawn out from the first inner space through the first opening when the drawer unit is in the second position. When the drawer unit is moved to the second position, a mounting space is formed for allowing the first transfer unit to be mounted in the second inner space.