A first box body is inserted between a first flat part and a first frame portion of a cover and is fastened to the cover by means of a first fastening member so that the first frame portion is interposed between the first box body and a plate-shaped first fixing member forming a first fixing member window for exposing a display section. A second box body is inserted between a second flat part and a second frame portion of the cover and is fastened to the cover by means of a second fastening member so that the second frame portion is interposed between the second box body and a plate-shaped second fixing member forming a second fixing member window for exposing an operation section.