PURPOSE: To contrive to improve the yield and the quality of a product by a method wherein the speed control in an injection process is corrected by an open loop control system and the pressure control in a pressure stabilizing process is corrected by a closed loop control system and the correction of the speed control is conducted by a step unit.

CONSTITUTION: The correction of the speed control in an injection process S is conducted in an area O by the open loop control system based on the measurement of injection speed at the specified places in the last injection, while the correction of the pressure control in a pressure stabilizing process H is conducted in an area C by the closed loop system to feedback the correction of the discrepancy from the specified value on the basis of the measurement of pressure applied to molten resin. The correction of the injection speed control is conducted in steps at the corrective value of about 1% of the target injection speed. Therefore, the oil pressure in the injection process is fixed mechanically and the speed control can be kept by only the opening of a flow control valve and inspite of the presence of factors to change injection speed at each such as scuffing of an injection piston etc. a good injection state can be obtained without any excessive correction.