To provide a motor controlling device that reduces heat generated by an armature and switching elements when an alternating motor is activated. A motor controlling device includes: an H bridge circuit 20 that has FET1 to FET4 that connect and disconnect a high potential end HV and a low potential end GND of a direct-current power supply to and from an armature Lu; and an energization control unit for controlling the amount of energization of the armature Lu by the PWM control that involves changing the ratio, in a predetermined control cycle, between an energization control period, in which the FET1 and the FET2 are turned on and the FET3 and the FET4 are turned off, or the FET3 and the FET4 are turned on and the FET1 and the FET2 are turned off, and a non-energization control period, in which the FET1 and the FET3 are turned on and the FET2 and the FET4 are turned off, or the FET2 and the FET4 are turned on and the FET1 and the FET3 are turned off.