A lid member has an external shape inscribing a quadrilateral formed by two sets of two facing sides, and has: a pair of first cut-out sections configured by cutting out, in the same size, a pair of diagonal corners from among the two sets of diagonal corners of the quadrilateral; and a pair of second cut-out sections configured by cutting out the other diagonal corners in the same size. The outer shape of the lid member is formed in a point-symmetric shape relative to the center of an opening in a peripheral wall section. The first cut-out sections have a larger surface area than the second cut-out sections, and one out of the pair of first cut-out sections is configured so as to be arranged in the vehicle progression direction and at the bottom in the vertical direction, when a base body is mounted to a vehicle.