To obtain good workability when filling a hydraulic oil into a tank through an opening formed on the upper portion of a reservoir tank without harming the performance of preventing hydraulic oil leakage and of preventing the mixture of air into a hydraulic circuit.

The reservoir tank 10 is assembled on a car body, accommodates a prescribed amount of the hydraulic oil inside, and has air communication passage Ap provided on its upper portion. This tank comprises two partition plates 13, 14, which divides the tank interior into up and down, at a desired intervals. A communication hole 14a penetrating in the vertical direction is formed at one end portion on the lower partition plate 14, and another communication hole 13a penetrating in the vertical direction is formed at the other end on the upper partition plate 13. In a state that the reservoir tank 10 is not inclined, at least the upper partition plate 13 is arranged above the oil surface Lo of the hydraulic oil accommodated in the reservoir tank 10. A pair of intake openings 21, 22 for a reversible electro-hydraulic pump 20 is provided at the bottom portion of the reservoir tank 10.