An electric motor control device comprising: an inverter that supplies an output of a primary-side DC power supply (18,22) to an electric motor to control driving of the electric motor; a converter that includes a voltage increasing power supply device (25,26,29) that increases a voltage of the primary-side DC power supply to supply the inverter with the increased voltage as a secondary voltage, and a regenerative power supply device that reversely supplies regenerative power from the inverter to the primary-side DC power supply; secondary-side target voltage determination means for determining a secondary-side target voltage 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 of the converter is applied to at least two phases and in which field weakening control is performed, and a second region 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 phases and in which field weakening control is performed; converter control means for controlling the voltage increasing power supply means and the regenerative power supply means of the converter such that the secondary voltage becomes the secondary-side target voltage; and electric motor control means for controlling the inverter on the basis of a target torque and a rotation speed of the electric motor and the secondary voltage such that an output torque of the electric motor becomes the target torque. an inverter that supplies an output of a primary-side DC power supply (18,22) to an electric motor to control driving of the electric motor; a converter that includes a voltage increasing power supply device (25,26,29) that increases a voltage of the primary-side DC power supply to supply the inverter with the increased voltage as a secondary voltage, and a regenerative power supply device that reversely supplies regenerative power from the inverter to the primary-side DC power supply; secondary-side target voltage determination means for determining a secondary-side target voltage 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 of the converter is applied to at least two phases and in which field weakening control is performed, and a second region 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 phases and in which field weakening control is performed; converter control means for controlling the voltage increasing power supply means and the regenerative power supply means of the converter such that the secondary voltage becomes the secondary-side target voltage; and electric motor control means for controlling the inverter on the basis of a target torque and a rotation speed of the electric motor and the secondary voltage such that an output torque of the electric motor becomes the target torque.