A gear made of a resin includes a substantially cylindrical rim having a plurality of teeth formed around an outer periphery thereof, a boss formed about a rotational center of the rim, and a web connecting the boss and the rim to each other. At least one groove is defined along outer surface of each tooth to divide the tooth in a widthwise direction of the tooth. As a result, a portion of the gear, in which the grooves are defined, is deformed in a reduced amount, leading to a reduced amount of deformation such as a warpage or sink in the entire gear, thereby providing an enhancement in tooth flank accuracy. Since the grooves are defined along the outer surfaces of the teeth, a lubricant such as grease can be supplied effectively to tooth flanks by previously applying the lubricant in the grooves.