To easily and surely arrange an oil tank device without interfering with the other devices by longitudinally arranging one or a plurality of tanks in a seat lower space formed at a lower part of seats arranged on a floor board, and laterally arranging the remained tanks on a floor board lower space continued therefrom.

A seat lower space 25 is formed at a lower part of the seats 18 arranged along a car body side wall 21 of a bus, and a floor board lower space 27 continued therefrom is formed between the seat lower space 25 and a longitudinal frame 13. A first oil tank 29 and a second oil tank are longitudinally arranged in adjacent to each other in the seat lower space 25. Further a gas tank 33 is laterally arranged in the floor board lower space 27. Whereby, the seat lower space 25 can be effectively utilized, and the oil tank devices can be collectively placed in compact. Further, by longitudinally placing the oil tanks, the inert gas can be effectively prevented from mixing in the oil and flowing from a low pressure hose 45 to a hydraulic oil pump.motor side.