Abstract: A plastic gear and a plastic compound gear that can endure excessive loads without degrading gear precision. In the plastic compound gear, both a large diameter gear and a small diameter gear have a plurality of ribs that are respectively connected to teeth root portions with the outer end portions thereof. The ribs are inclined to one side (counterclockwise) in the circumferential direction viewed from a longitude line that passes through the gear center. Therefore, when the compound gear used as a drive gear with respect to two secondary gears are rotated about a boss counterclockwise to rotate the secondary gears clockwise, the inclination of the ribs works against the force that is applied to the teeth root portion.

Abstract: A plastic gear includes a teeth part formed on its outer periphery, a web formed on the inner side of the teeth part and a plurality of ring-shaped rims concentrically formed such that the web is divided into a plurality of ring-shaped webs in a concentrically circular shape. The plurality of ring-shaped webs includes two or more ring-shaped webs without rib which has no ribs connecting adjacent ring-shaped rims on an outer peripheral side other than the ring-shaped web to which gates for resin molding are to be disposed at the time of resin molding.