A cooling system is equipped with a circulation flow path arranged to flow a coolant into an engine, a motor drive system flow path branched off from the circulation flow path and arranged to flow the coolant into a motor drive system, a flow rate distribution regulator provided at a junction of the circulation flow path and the motor drive system flow path, and an electric pump configured to pressure-feed the coolant through the circulation flow path. In the cooling system, the procedure of flow rate control sets an engine flow rate demand Vwe based on a rotation speed Ne and a torque te of the engine and a coolant temperature Te (step S110), while setting a motor flow rate demand Vwm based on an inverter current Iinv of the motor drive system and the coolant temperature Te (step S120). The flow rate distribution regulator and the electric pump are then controlled to make a flow rate of the coolant flowed into the engine and a flow rate of the coolant flowed into motors and inverters included in the motor drive system respectively equal to the set engine flow rate demand Vwe and the set motor flow rate demand Vwm (steps S130 and S140).