A gear made of a resin including a cylindrical toothed portion formed at a radially outer location, a shaft-supporting section formed at a radially inner location around the rotational center of the toothed portion, and a thin plate-shaped web connecting the shaft-supporting section and the toothed portion to each other, wherein the web has a circumferential rib concentric with the toothed portion inside the toothed portion, and a plurality of diametrical ribs diametrically connecting the circumferential rib and the shaft-supporting section to each other along the side of the web, each of the diametrical ribs being formed by a first diametrical rib portion extending obliquely in a direction opposite from a normal rotational direction from the outer periphery of the shaft-supporting section, and a second diametrical rib portion extending obliquely in a direction opposite from an opposite rotational direction from the outer periphery of the shaft-supporting section.