The present disclosure provides an inverter control device for estimating the magnetic flux of a rotor, and calculating and compensating for a slip frequency on the basis of a torque current and a magnetic flux current, to control the speed of an electric motor. To this end, the present invention may comprise: a command voltage generation unit for outputting a three-phase PWM voltage with respect to a command frequency to an inverter on the basis of voltage/frequency operation; and a slip frequency determination unit for determining a slip frequency on the basis of the phase current and phase voltage of an electric motor driven by the inverter.