A gear 1 made of a resin includes webs 5 (5a and 5b) formed so that the rigidity of the web is increased by a first circumferential rib 8, a second circumferential rib 10, first diametrical ribs 11 and second diametrical ribs 12, and the circumferential sectional shape of the outermost web 5c is a corrugated shape, whereby the rigidity of the outermost web 5c is increased. As a result, it is possible to increase the rigidity of the outermost web 5c without increasing of the thickness of the outermost web 5c; to form a toothed portion 6 with a high accuracy; to reduce the deformation (for example, the amount of displacement of the toothed portion 6 and a shaft-supporting portion 4 in a rotating direction) due to an external force; and to enhance the rotation-transmitting accuracy. In this gear 1, a vibration and a noise due to the vibration can be reduced by increasing the rigidity of the web.