PURPOSE: To improve startability of a generator, by passing a cooling-water circuit for cooling an engine for driving a generator through a heat exchanger connected to an exhaust pipe of the engine of a mobile generator vehicle.

CONSTITUTION: A heat exchanger 8 is connected to an exhaust pipe of an engine 7 for driving a mobile generator vehicle 6, and a cooling-water circuit for an engine 1 for driving a generator is passed through the heat exchanger 8. A thermostat 10 and a three-way valve 11 are provided at an intermediate portion of the cooling-water circuit. With such an arrangement, water heated by the heat exchanger 8 is carried into the engine 1 via a passage C and warms up the engine 1, while low-temperature water in the engine 1 is carried from a passage A to a passage B by the function of the thermostat 10 and then carried into the heat exchanger 8 via a passage E. When the engine 1 is warmed up, the three- way valve 11 is controlled to pass water in a direction F. Thus, since the generator engine 1 is warmed up by use of the exhaust gas of the engine 7 for driving the self-driven vehicle 6, it is enabled to improve startability of the engine 1 at the time when the temperature is low.