To make an outer frame used in common by using a front frame with a cover member and a front frame without a cover member.

A front frame 2B is so constructed that a cap-like cover member 6B is fixed to the corner part of a plate-like front frame main body 20 to cover four faces of the front and rear and the sides of the corner part. In the front frame, a recessed part 7 set to a depth above the thickness of a rear piece 60c of the cover member 6B is provided corresponding to the rear piece 60c of the cover member 6B on the back of the corner part of the front frame main body 20. The front frame 2B has the rear piece 6c of the cover member 6B housed in the recessed part 7, so that the corresponding outer frame is shaped in the same manner as the resin-made front frame.