A holding portion 12 has a shape which allows relative movement between a pivot portion 21 and the holding portion 12 in the radial direction of the pivot portion 21 such that cover 20 is attachable to, and removable from, a cabinet 11 in the radial direction of the pivot portion 21. An engaging member 50 is movable between a locked position and a unlocked position. At the locked position, the engaging member 50 engages with the cabinet 11 so as to restrict the relative movement between the pivot portion 21 and the holding portion 12. At the unlocked position, the engaging member 50 releases the engagement between the engaging member 50 and the cabinet 11. A stopper 13 restricts the movement of the engaging member 50 from the locked position to the unlocked position.