To obtain a cast product having high strength and a dense structure and to reduce the failure of oil leakage, etc., by increasing the pressurizing force and the pressurizing vol. of an Acurad process pin.

In an injecting device, in the case of incorporating a piston 21 working an Acurad pin 19 into the inner part of an injecting piston 14, the back surface of the piston 21 for the Acurad pin is made to the same chamber with the back surface of a piston for a plunger. A working oil supplying pipe is fixed to the cover of an injecting cylinder 9 and side to the piston 21 for the Acurad pin and fitted so as to seal and a passing hole is opened in a piston rod 2 so as to be able to supply/discharge the oil in the chamber at the rod side of a cylinder 20 for the Acurad pin. By this constitution, the structure and the operarion are made simple and the volume and the force are increased by enlarging the built-in cylinder.