PURPOSE: To make the boosting time after final filling adjustable to arbitrary time irrespectively of the metering accuracy, temp., etc. of molten metal by operating the pilot check valve in parallel with a flow metering valve on injection cylinder side by the pressure on injection cylinder piston side.

CONSTITUTION: The molten metal 19 supplied into an injection cylinder 11 is filled into a die cavity by a plunger tip 14 which is driven by an injection cylinder 12. Upon completion of the filling, the tip 14 stops, and the pressure P1 in a chamber A rises. At this time, a flow metering valve 17 is connected to a chamber B, so that a back pressure P2 acts. The pressure acting upon the metal 19 is (P1-P2). Here, if a sequence valve 15 having beforehand been set equal to the filling completion pressure operates, a pilot check valve 16 opens to make P20, and finally P=P1, that is, after the final filling, the pressure P is boosted. In the case of adjusting the pressure increasing time by the kinds and temps. of the metal 19 and the shapes, temps., etc. of dies, the speed of opening of the valve 16 can be adjusted by a flow metering valve 18, and the degree of opening of the valve 16 is made easily adjustable with respect to time.