PURPOSE: To provide a hydraulic power unit capable of correctly controlling hydraulic power as well as easily discovering gas pressure abnormality of an accumulator.

CONSTITUTION: This is a hydraulic power unit A provided with a motor 1, a pump 3 and an injection type accumulator 5 which pumps up oil from a tank 7 by way of driving the pump 3 with the motor 1 and supplies this oil to an actuator 9. A pressure sensor 25 to detect change of gas pressure is connected to a gas chamber 5a of the accumulator 5. A control unit 17 to control the hydraulic power unit A is electrically connected to this pressure sensor 25.