A control device which includes a power conversion circuit configured to supply driving power to an electric motor, a magnetic flux estimation circuit configured to estimate a primary magnetic flux of the motor, and a voltage command generation circuit (control circuit) configured to control the conversion circuit based on an estimation result of the primary magnetic flux, in which the estimation circuit performs, when an operating speed of the motor is less than a predetermined level, a first estimation of estimating the primary magnetic flux based on an output current to the motor and an inductance thereof, and performs, when the speed exceeds a predetermined level, a second estimation of estimating the primary magnetic flux by estimating a magnetic flux differential value based on an output voltage of the conversion circuit and integrating the value using, as an initial value, an estimation result by the first estimation.