A base portion includes a cam surface formed around a support pin. A turning portion includes: a slide member provided movably in directions toward and away from the support pin; and a coil spring urging the slide member. The slide member is designed to slide on the cam surface while turning, together with an openable body, about the support pin. The cam surface includes a first sliding surface, a second sliding surface, and a third sliding surface. The first sliding surface presses the slide member back in a direction of closing of the openable body. The second sliding surface presses the slide member back in a direction of opening of the openable body. The third sliding surface presses the slide member back in the direction of closing of the openable body.