PURPOSE: To prolong the life of metal mold and enable good-quality products to be readily obtained by injecting all strokes under low pressure and injecting the greater portions of the strokes and the final small stroke portions respectively under the specified casting pressure by the operation of limit switch.

CONSTITUTION: The device consists of an injection cylinder 1, electromagnetic changeover valves 3, 10, high-pressure accumulator 4, high-pressure line 8, low- pressure line 9, limit switch 12, etc. All the strokes of injection are regulated to low speeds of about 0.3W0.4m/sec. by way of a regulating valve 5 and the greater portions of the injection strokes are injected under casting pressures of 300W800kg/cm2 by regulating the set pressures of the accumulator 4 and regulating valve 11. The smallest stroke portions (1W2mm) are injected under pressures of 80W200kg/cm2. The above-mentioned changing-over is accomplished by the solenoid valve 10 for changing over of the high-low-pressure lines 8, 9 interlocking to a limit switch 12 by the operation of a piston rod 2. It is also equally well to separately provide high- and low-pressure accumulators and connect these to the cylinder head side 1a by way of an electromagnetic changeover valve. The life of metal mold is prolonged because casting pressure is low.