There is disclosed a die used to mold a cage having a cylindrical body out of a synthetic resin such that the strength of the portion of the molded cage formed by two meeting streams of the injected material is increased. The die comprises die members having parting surfaces in abutment with each other. A mold cavity conforming in shape with the cylindrical body of the cage is formed between the die members. When the die members, are in abutment with each other, a gate and a resin reservoir are formed along one parting surface and outside the mold cavity. The gate and resin reservoir are in communication with the cavity.