A bearing, for supporting a rotation shaft of a rotatable member, capable of being supported by a supporting portion provided with an engaging hole engageable with the bearing includes positioning projections having contact surfaces and bearing projections having sliding surfaces on which an outer peripheral surface of the rotation shaft slides. The positioning projections project from different positions so that between adjacent positioning projections, an outer peripheral surface of the bearing and the inner wall surface of the engaging hole form a gap therebetween. The bearing projections project from different positions so that between adjacent bearing projections, an inner peripheral surface of the bearing and an outer peripheral surface of the rotation shaft form a gap therebetween. With respect to a circumferential direction of the rotation shaft, the positioning projections and the bearing projections are provided at positions different from each other.