A controller of a multi-phase electric motor comprising: drive means, including a pair of an upper arm switching element and a lower arm switching element, for driving the multi-phase electric motor; single current detection means, provided between a direct current power supply and the drive means, for detecting a current value of the multi-phase electric motor; PWM signal generation means for generating plural PWM signals of each predetermined motor phase within one control period based on the current value detected by the current detection means and a carrier signal, one control period including plural periods of the PWM signal of each predetermined motor phase; current detectability determination means for determining whether or not the current value is detectable in the current detection means based on the PWM signal of each predetermined motor phase generated by the PWM signal generation means, and phase movement means for moving the PWM signal of a predetermined motor phase generated by the PWM signal generation means by gradually changing a value of a shift amount of the phase in one control period by setting the shift amount in each of said plural periods of one control period to a different value, and outputting the resultant PWM signal to the drive means; the phase movement means being adapted to move the PWM signal of the predetermined motor phase generated by the PWM signal generation means when the current detectability determination means determines that the current is not detectable, wherein the phase movement means is adapted to, if a value of a shift amount of the phase of the predetermined motor phase in a control period immediately before a control period of this time is zero, and a value of a shift amount of the phase of the predetermined motor phase in the control period of this time is not zero, increase a value of a shift amount in each of said plural periods of the control period of this time so that the value of the shift amount gradually increases from zero in the control period of this time, and wherein the phase movement means is adapted to, if a value of a shift amount of the phase of the predetermined motor phase in the control period immediately before the control period of this time is not zero, and a value of a shift amount of the phase of the predetermined motor phase in the control period of this time is zero, decrease a value of a shift amount in each of said plural periods of the control period of this time so that the value of the shift amount is gradually decreased to become zero in the control period of this time. drive means, including a pair of an upper arm switching element and a lower arm switching element, for driving the multi-phase electric motor; single current detection means, provided between a direct current power supply and the drive means, for detecting a current value of the multi-phase electric motor; PWM signal generation means for generating plural PWM signals of each predetermined motor phase within one control period based on the current value detected by the current detection means and a carrier signal, one control period including plural periods of the PWM signal of each predetermined motor phase; phase movement means for moving the PWM signal of a predetermined motor phase generated by the PWM signal generation means by gradually changing a value of a shift amount of the phase in one control period by setting the shift amount in each of said plural periods of one control period to a different value, and outputting the resultant PWM signal to the drive means;