A resin injection molding method uses a mold having a cavity and a hole-forming columnar body. The hole-forming columnar body is movable in an axial direction while extending through the cavity, and includes a first diameter portion having a first diameter, a second diameter portion having a diameter greater than the first diameter, and a tapered portion having a diameter gradually increasing from the first diameter portion toward the second diameter portion. The method includes moving the hole-forming columnar body in the axial direction such that at least one of the first diameter portion or the tapered portion is positioned in the cavity, injecting the molten resin to fill the cavity, maintaining an inside of the cavity under pressure, moving the hole-forming columnar body in the axial direction such that the second diameter portion is positioned in the cavity, and solidifying the injected filling molten resin.