To stabilize the fluctuation in the ram speed in the initial extrusion in an early stage by performing the ram speed control when the peak pressure in a main cylinder is detected during the pressure control of the main cylinder.

In the main cylinder pressure control PCA, a switching means 10e of a CPU 10 is operated to be connected to a second operating means 10c when the detected value of a pressure detector 8 becomes the peak, the command value to boost the moving speed of a ram 2 at the prescribed pattern is outputted by a ram speed setting device 12, and switching is performed to the ram speed control SCA. The command value from the ram speed setting device 12 is compared with a second comparator 10d to obtain the deviation. The deviation is converted into the valve opening adjust amount by the second operator 10c, and outputted to a comparator 7e of a valve means 7. The opening amount of a valve disk 7b is adjusted according to the deviation between the detected value of a valve opening detector 7d and the valve opening regulation quantity.