Abstract: A method for producing an injection molded article including a highly-filled fiber-reinforced resin composition includes a step of charging a first resin feedstock including a thermoplastic polymer into an injection molding machine through a first inlet port; a step of charging a second resin feedstock into the injection molding machine through a second inlet port disposed downstream of the first inlet port, the second resin feedstock including a masterbatch that includes long fibers impregnated with a resin mixture including a thermoplastic polymer and an acid-modified polyolefin; a step of melt-kneading the first resin feedstock and the second resin feedstock together in the injection molding machine to give a fiber-reinforced resin composition melt; and a step of injection molding the fiber-reinforced resin composition melt in a mold, the first resin feedstock being charged intermittently or continuously from the start to the end of the charging of the second resin feedstock.