To prevent an actuator or a mold from being impaired by a method wherein when a position of a valve rod of a servo valve controlling an actuator is detected, and the position is deviated from a preliminarily determined range, counting of a timer is started, and when a specific set time has elapsed for the timer, an abnormality signal is outputted from a controller.

When valve rod control signals 13, 14 of a servo valve 10 are at zero volt, the valve rod comes to be of a breaking off state for all four ports. When the valve rod control signal 14 is increased to a plus side, the valve rod is changed, for example, right, and the valve rod control signal 13 also is increased to a plus side according to a valve of the valve rod control signal 14 following that. When polarities of the valve control signals 13, 14 agree with each other, and the valve rod is not changed to a specific position, or when it is changed to more than the specific position, a controller 15 starts a timer. Then, when the timer executes time up, an abnormality signal is outputted, a power source of an electric motor driving a hydraulic pump constituting a hydraulic source 12 is cut off, and a cartridge valve 11 between the hydraulic source 12 and the servo valve 10 is closed.