An opening and closing mechanism includes a fixed member which has a fixed cam on its side face; a movable member which has a movable cam on an opposing face to the fixed cam, and which is rotatably disposed relative to the fixed member; a case housing the fixed member and the movable member; and a spring applying a force toward the fixed member to the movable member. The movable member has a recess at its radial center, and the first end of the spring is inserted in this recess.