Abstract: A hydraulic pressure source includes an oil tank for storing hydraulic oil, a hydraulic pump, a motor for driving this hydraulic pump, and an inverter for changing a rotational frequency of the motor. A pipe line for drawing the hydraulic oil from the oil tank by operation of the hydraulic pump branches to a supply pipe line for supplying the hydraulic oil to the hydraulic cylinder, and a release pipe line for releasing superfluous hydraulic oil into the oil tank. The release pipe line has arranged thereon a pressure regulating mechanism and a flowmeter which measures a flow rate of the hydraulic oil flowing into the release pipe line. Based on a measurement value of the flowmeter, the inverter is operable to change the rotational frequency of the motor to become a necessary minimum rotational frequency.

Abstract: A hydraulic pressure source includes an oil tank for storing hydraulic oil, a hydraulic pump, a motor for driving this hydraulic pump, and an inverter for changing a rotational frequency of the motor. A pipe line for drawing the hydraulic oil from the oil tank by operation of the hydraulic pump branches to a supply pipe line for supplying the hydraulic oil to the hydraulic cylinder, and a release pipe line for releasing superfluous hydraulic oil into the oil tank. The release pipe line has arranged thereon a pressure regulating mechanism and a flowmeter which measures a flow rate of the hydraulic oil flowing into the release pipe line. Based on a measurement value of the flowmeter, the inverter is operable to change the rotational frequency of the motor to become a necessary minimum rotational frequency.