The present invention comprises a speed feedback control system for carrying out speed feedback control on the basis of a speed detected value Vd obtained by converting a position detected value Xd obtained from a screw position sensor 4, a pressure feedback control system for carrying out a pressure feedback control on the basis of a pressure detected value Pdb obtained from an injection pressure sensor 6b, and a VP switching control function portion Fc for carrying out switching from a speed control region to a pressure control region Zp when a pressure deviation Ep between a preset pressure set value Ps and the pressure detected value Pdb becomes a preset switching determination value Eps or less and carrying out the switching to the pressure control region Zp after control of a speed command value in the speed control region Zv by a predetermined control pattern Dp at this switching.