While a second layer resin is being charged, a movable platen is moved backward to reach a given movable platen position (S1) to enlarge the capacity of a second cavity. After the completion of charging of the resin, a toggle mechanism is promptly driven to reduce the second cavity capacity to reach a given movable platen position (S2), and after the lapse of a given time, the toggle mechanism is driven again to enlarge the second cavity capacity to reach a given movable platen position (S3). Thus, a high quality multilayer injection molded article which has small variations in the wall thickness, dimension, and mass and which is free from deformation or warpage can be stable obtained.