To protect a battery for driving a pump as a power source of a motor and assure safe working conditions, without sudden intermission of the work with a hydraulic machine.

A vehicle, loading a hydraulic machine 10 which is operated as a hydraulic source with a hydraulic pump 13 driven by an engine 11 and the motor 15, is provided with a voltage-detecting means for detecting a voltage of a pump driving battery E2 and a control means for continuing; and while the hydraulic machine 10 is operated with the motor 15, with the operation of the hydraulic machine 10, even if the voltage of the pump driving battery E2 becomes lower than the prescribed voltage and for shutting off, when the hydraulic machine 10 once stops the operation and thereafter it re-started of the operation of a circuit of the motor 15 and drives an engine 11 to change over the operation of the hydraulic machine 10 with the engine 11.