A controller for a motor is capable of reducing the amount of energization required to operate a motor under a predetermined condition, the motor having two rotors disposed around a rotating shaft. The controller includes an induced voltage constant command value determiner which determines an induced voltage constant command value (Ke_c) of a motor such that a difference (ΔVp) between a target voltage circle radius (Vp_target) and a magnitude (Vp) of the vector sum of a d-axis voltage command value and a q-axis voltage command value of the motor decreases, a rotor phase difference acquirer and a rotor phase difference command value determiner which change a rotor phase difference on the basis of the Ke_c, and a field weakening current correction value calculator which determines a field weakening correction current ΔId_vol on the basis of ΔVp and adds the determined ΔId_vol to the d-axis current command value in the case where Vp cannot be reduced to Vp_target or less by reducing Ke_c to a lower limit of a rotor phase difference changing range.