The present invention is intended to provide a method for manufacturing a resin gear with a core metal by which there is no reduction in strength even with gates allowing decrease in material costs such as pin gates in the molding die for injection molding.The manufacturing method includes: gates at a primary molding step and gates at a secondary molding step are pin gates or the like. The number of the gates at the primary molding step and the number of the gates at the secondary molding step are plural and identical, and the gates are arranged circumferentially. Gate positions G21, . . . at the secondary molding step are circumferentially intermediate or nearly circumferentially intermediate between gate positions G11, . . . and weld positions W11, . . . adjacent to the gate positions G11, . . . in the primary molded article.