The main body frame includes a first frame including a flexible protruding plate portion, a second frame facing the first frame in a first direction to form the housing section, and a snap-fit mechanism connecting the first frame to the second frame. The snap-fit mechanism includes a fitted portion provided on the flexible protruding plate portion and a fitting projection portion provided on a side wall of the second frame and fitting with the fitted portion. The fitting projection portion and the fitted portion are fitted by bringing the first and second frames into relative proximity in the first direction, and the fitting is released by relatively displacing the first and second frames in a second direction orthogonal to the first direction.