Abstract: In an injection molding method, a resin is injected into a cavity of a mold in such a manner that a pressure ratio of a cavity surface pressure in the cavity to a cylinder pressure of an injection molding device is not less than 0.65, a first pressure keeping process to keep the cylinder pressure at a constant is conducted after the filling step, the cylinder pressure is increased so that the cavity surface pressure in the cavity is 0.95 times or more larger than the pressure at the time that the cavity has been filled with the resin; and a second pressure keeping process to keep the changed increased pressure at least until a cavity surface temperature becomes lower than a glass transition temperature of the resin.