An electric motor controller to control an electric motor through an inverter configured to convert an inputted power by use of a switching unit and to output the converted power, the electric motor controller comprising: a current detection unit configured to detect a current supplied to the electric motor as a current detection value; and a control unit configured to perform a control operation in a cycle based on a carrier frequency of a carrier signal, wherein the control unit includes a current control part configured to calculate a voltage command value of a voltage to be applied to the electric motor, a drive signal generation part configured to generate a drive signal for driving the inverter by comparing the voltage command value outputted from the current control part with the carrier signal, and a carrier frequency command part configured to instruct switching of the carrier frequency of the carrier signal, the current control part includes a feedback control part (43a, 43b, 43i) configured to calculate the voltage command value through feedback control using the current detection value; characterized by a disturbance estimation part (43c, 43d, 43e, 43f) configured to estimate a disturbance component on the basis of the current detection value and the voltage command value and add the estimated disturbance component to the voltage command value to be outputted to the drive signal generation part, and in a case where the carrier frequency is switched, the disturbance estimation part (43c, 43d, 43e, 43f) configured to update a control constant that is used for the disturbance estimation and is dependent on a control operation cycle, in a control operation performed in a cycle later than a control operation immediately after the switching of the carrier frequency. a current detection unit configured to detect a current supplied to the electric motor as a current detection value; and a control unit configured to perform a control operation in a cycle based on a carrier frequency of a carrier signal, wherein the control unit includes a current control part configured to calculate a voltage command value of a voltage to be applied to the electric motor, a drive signal generation part configured to generate a drive signal for driving the inverter by comparing the voltage command value outputted from the current control part with the carrier signal, and a carrier frequency command part configured to instruct switching of the carrier frequency of the carrier signal, the current control part includes a feedback control part (43a, 43b, 43i) configured to calculate the voltage command value through feedback control using the current detection value; characterized by a disturbance estimation part (43c, 43d, 43e, 43f) configured to estimate a disturbance component on the basis of the current detection value and the voltage command value and add the estimated disturbance component to the voltage command value to be outputted to the drive signal generation part, and in a case where the carrier frequency is switched, the disturbance estimation part (43c, 43d, 43e, 43f) configured to update a control constant that is used for the disturbance estimation and is dependent on a control operation cycle, in a control operation performed in a cycle later than a control operation immediately after the switching of the carrier frequency.