In an image forming device, at an end portion of a middle frame, a first protrusion and a second protrusion are arranged so as to protrude substantially parallel to each other. A plate-shaped arm extends from a leading end of the second protrusion in a direction towards a leading end of the first protrusion. A control protrusion is integrally arranged at a leading end of the plate-shaped arm. On the other hand, a rear side frame has a recessed portion. When the first protrusion, the second protrusion, and the plate-shaped arm are inserted into the recessed portion, the control protrusion passes a latching protrusion provided to the recessed portion, and the control protrusion and the latching protrusion are latched by facing each other.