PURPOSE: To stabilize a hydraulic operating system during the pressure accumulating-holding time of accumulators in an oil pressure supply device constituted in such a way as to accumulate-hold operating oil in the accumulators at the time of reducing the discharge pressure of a variable dis placement pump according to the supply pressure required by load and to supply the operating oil effectively at the time of increasing the discharge pressure.

CONSTITUTION: An oil pressure supply device is provided with a supply pressure line 26 reaching load 1 from a variable displacement pump 4, and a change-over valve 7 capable of communicating or cutting off between a first accumulator 10 and a third accumulator 41. At the time of normal discharge pressure, the first accumulator 10 is communicated, and only at the reduced time of discharge pressure, the communication with the third accumulator 41 is performed.