A primary-side DC voltage is increased to a secondary voltage by a converter (30c), and converted by an inverter (19) into three-phase AC, which is applied to an electric motor (10m). Regenerative power from the electric motor is reversely supplied to a primary-side DC power supply (18, 21).
A secondary-side target voltage, which sets the secondary voltage to be applied to the inverter, is determined such that the electric motor is driven on the basis of one of a first region in a modulation mode in which PWM power is applied to at least two phases and in which field weakening control is not performed, a third region in a modulation mode in which PWM power at a voltage lower than a maximum voltage (Vmax) that can be output by the converter is applied to at least two phases and in which field weakening control is performed, and a second region ( FIG. 4 ) in a one-pulse mode in which rectangular-wave power at a voltage lower than the maximum voltage of the converter is applied to all the phases and in which field weakening control is performed. A converter control device (30v) controls the secondary voltage to the secondary-side target voltage.