A primary molding product is formed by integrally forming a first lead frame and a second lead frame with a primary molding resin portion. In addition, in order to prevent separation of the first lead frame and the second lead frame from the primary molding resin portion, a hook-and-hold portion for preventing separation of the first lead frame from the primary molding resin portion and separation of the second lead frame from the primary molding resin portion is provided on an outer surface of each of the first lead frame and the second lead frame. Thus, a resin molding part capable of achieving suppression of increase in a thickness thereof without deformation or displacement of a lead frame and a manufacturing method thereof can be provided.