Abstract: An injection molding method includes a holding step, a cavity forming step, a first injection step, a compression molding step, and a second injection step. In the holding step, a skin layer is held under tension by tension pins. In the cavity forming step, a male mold and a female mold are disposed in facing relation to each other, forming a molding cavity therebetween with a gap between the male and female molds being grater than the thickness of a door trim (body of synthetic resin) by a predetermined distance. In the first injection step, a molten synthetic resin is injected from a first injection gate into the molding cavity. In the compression molding step, the male mold and the female mold are displaced toward each other by the predetermined distance, compression-molding an upper portion (first portion) of the door trim of the molten synthetic resin.