A pump motor of a hydraulic hybrid system also serves as a pump to supply hydraulic oil or lubricating oil to a power train, thus enabling elimination of an oil pump provided in the power train and hence reductions in the number of parts and cost, and, in addition, an existing oil pan provided in the power train and the like are utilized for the hydraulic hybrid system, which in turn enables achieving further reductions in the number of parts and cost. Moreover, when idle-reduction control is performed on an engine, during engine's stopped conditions, the pump motor can be driven as a motor by hydraulic pressure accumulated in an accumulator to start the engine and supply the hydraulic pressure to a transmission, thus eliminating a need to provide a motor-driven oil pump for the idle-reduction control and hence enabling a further reduction in cost.