The invention is provided with a first injection electric motor used for low-speed injection and increasing pressure, a second injection electric motor used for high-speed injection, first and second power transmission mechanisms for transmitting rotary motion of the injection electric motors to a screw shaft, first and second clutch mechanisms provided in the power transmission mechanisms, an injection plunger advanced and withdrawn integrally with respect to a nut threaded on the screw shaft, and a controller for controlling the driving of the injection electric motors and the clutch mechanisms. The controller starts the second injection electric motor from a stopped state before the point in time where the high-speed injection step is to commence; and switches the second clutch mechanism from a disengaged state to an engaged state at the point in time where the high-speed injection step is to commence, or at a requisite timing prior thereto.