A resin gear includes a web with a side surface on which a first annular rib and a second annular rib are formed to be concentric with a boss. The web has an inner web portion coupling the first annular rib to the second annular rib, and an outer web portion coupling the second annular rib to a rim. The inner web portion is formed to have a thickness gradually reduced from one intersection point toward another intersection point, the intersection points being intersection points of a virtual radial direction line passing through a center of the boss with the second annular rib. The first annular rib has a side surface on which only one gate mark of an injection molding is formed at a position on a radially outer side with respect to a first tooth portion and a position biased to the other intersection point on the virtual radial direction line.