To provide a seal ring made of a resin not broken by expansion at the time of incorporation and having no trouble from an aspect of a shape such as burr or the like even if post processing is not performed.

The seal ring made of the resin has mutually opposed cut parts and a gate mark at injection molding. The gate mark is provided at a position separated from the opposed position of the cut parts by ≥90° but <180° as the center angle of the seal ring when the opposed position of the cut parts in a butted state is set to 0°. The seal ring is a molded product injection-molded using a mold wherein a resin sump is provided between the gate mark and the cut part on the side near to the gate mark through a resin sump inflow part and the shape of the resin sump inflow part is set so that the inflow resistance to the resin sump becomes higher than that to the seal ring part and the size of the resin sump is larger than a size perfectly filled simultaneously with the seal ring part at injection molding.