In a device substrate attachment structure, when a substrate including a terminal holder attached to an end portion thereof is attached to a frame made of sheet metal, the substrate is attached to the frame via the terminal holder without using a screw fastening structure. The terminal holder is attached to the frame via an engagement/disengagement mechanism. The engagement/disengagement mechanism includes through-hole portions on a side of the frame, a seat portion, claw portions, and leg portions on the side of the terminal holder, and a positioning mechanism on the side of a cabinet. The positioning mechanism includes rim portions of an opening window of the cabinet.