PURPOSE: To enhance rising stability at the starting time of operation and continuous molding stability by a method wherein a shot injection condition on and after the next time is allowed to approach the injection condition corresponding to proper injection graph pattern data when the present shot injection graph pattern data exceeds a tolerant range from the proper injection graph pattern data.

CONSTITUTION: When a graph pattern comparing part 27 judges that the present shot graph pattern data exceeds a tolerant range from proper graph pattern data, an injection command set value operation/alteration part 28 operates and forms the finely divided data relating to an injection speed at every stroke divided from a dividing way of an injection stroke and the finely divided data relating to pressure at every time divided from a dividing way of a time at the time of a pressure holding process to supply both data to an injection condition setting part 29. On the basis of the control signal from the injection condition setting part 29, the advance speed of a screw 10 and injection pressure are subjected to open control through an output interface 18 and amplifiers 19, 20.