To improve the mountability of a pressurized oil tank for an accumulator type energy regenerative apparatus and a prevention against the suction of gas into oil.

A pressurized oil tank T is formed into a cylindrical rectangular type hollow body, and the inside is longitudinally divided by a partition plate Ta into an oil chamber 1 and a gas chamber 2, and one end of a communicating tube 5 is connected to an apex of the oil chamber 1, and the other end is connected to a bottom part of the gas chamber 2. Mountability onto a vehicle becomes bettered by this rectangular type tank, therefore according to the expedient of a connecting method of this communicating tube 5, the suction of gas into oil and any possible cavitation in a hydraulic pump motor are all preventable.