A surge voltage generated by the switching operation of an IGBT element and voltage variation generated in an equivalent series resistance of a capacitor are superimposed on an input voltage of an inverter. The equivalent series resistance has a temperature dependence that a resistance value increases with a decrease in a capacitor temperature. The IGBT element has a temperature dependence that an element withstand voltage decreases with a decrease in an inverter temperature. When capacitor temperature is lower than a predetermined threshold value, a control device reduces an upper limit value of the input voltage by an amount corresponding to the voltage variation from its upper limit value at a high temperature, and controls a target voltage of a boost converter such that an output voltage does not exceed the upper limit value. Consequently, the allowable range of the surge voltage can be ensured.