PURPOSE: To assure specified gaseous pressure and oil volume from the start of work and to stabilize operation by providing a control valve and a temp. detector in a circuit for supplying working oil of an accumulator, and making the gaseous pressure regulable according to the change in the temp. of the working oil and gas.

CONSTITUTION: A titled device consisting of an accumulator combining a piston type accumulator 5 and a gas accumulator 6, a control valve 20 provided with a circuit for supplying working oil to the accumulator 6, and a temp. detector 21 which detects the temp. of the working oil or the temp. of the gas in the accumulator 6. Said control valve 20 controls the supplying and discharging of the working oil to and from the accumulator 6 in accordance with the output signal from the detector 21. The stable operation is carried out from the start of work by the above-mentioned device.