A gas-introduced injection molding is disclosed, which is obtained by charging molten resin into a die and introducing gas into the charged molten resin. The molding thus obtained has a sufficient thickness portion extending linearly as a framework and a sheet-like small thickness portion integral with the sufficient thickness portion and having a uniform thickness, a space being formed inside the sufficient thickness portion. Thus, even by reducing the overall thickness of the molding it is possible to ensure sufficient rigidity with the hollow portion, and the molding is thus best suited as a sheet-like product requiring a predetermined rigidity, such as an automobile bumper, a household electric product casing, etc. Such gas-introduced injection molding is produced by a method, which comprises a first step of charging molten resin into the die when the die is open to a predetermined extent from the completely closed state, a second step of closing the incompletely closed die to cause spreading of the charged molten resin, and a third step of introducing gas into the charged molten resin in the die. The second and third steps are started before the end of the first step. The molten resin in the die is thus caused to move continuously until the completion of the molding, thus preventing the generation of hesitation mark or sink mark.