In a configuration in which an auxiliary power supply is connected to an intermediate link circuit of a main conversion unit, intermediate link voltage as input voltage of the auxiliary power supply is set at higher voltage depending on the main conversion unit as a main unit, and loss generated in a main circuit element of the auxiliary power supply increases; therefore, a problem has occurred that a cooling unit has to be increased in size. The main conversion unit recognizes a low-speed and stop state by monitoring a vehicle speed, and varies the intermediate link voltage corresponding to the vehicle speed; thereby, the loss generated in the main circuit element of the auxiliary power supply is reduced at the low-speed and stop state where cooling ability is decreased; as a result, small sizing and light weighting of the cooling unit is achieved.