Provided is a resin composition for injection molding including a polyolefin resin, containing: at least one selected from the group consisting of aluminum hydroxide, magnesium hydroxide and a phosphorus compound in an amount of 10 to 60 mass %; a NOR-type hindered amine compound in an amount of 0.05 to 5 mass %; and a fibrous filler having an aspect ratio of 10 or more in an amount of 1 to 20 mass %, respectively, relative to the total amount of the resin composition, wherein a phosphorous content is 5 mass % or less relative to the total amount of the resin composition.