To enable the improvement in installment performance and energy saving through miniaturization.

Pressurized fluid is supplied respectively to a closing cylinder 23, a metering motor 33, an injection cylinder 41, a nozzle moving cylinder 53 and a protruding cylinder 62 by driving a hydraulic pump 15 by a hydraulic actuator A comprising an accumulator 8 for generating a substantially constant pressure, a volume variable type hydraulic device 1 connected to the accumulator, a volume operating device 12 for changing the volume of the hydraulic device 1 and a control device 10 for sending an operating signal in accordance with a control instruction thereof, whereby regenerative energy is regenerated at the accumulator for energy saving and the miniaturization of a hydraulic device is realized by means of the hydraulic actuator A having a power density higher than servo motors and motor drivers having substantially identical outputs.