A control device controls an inverter controlling an output of a motor by PWM control. The control device calculates a reference frequency (fs) based on a torque and a rotation speed of the motor, calculates a random coefficient (±) using two data tables, and calculates, as a random frequency (fr), a value obtained by adding, to a reference frequency (fs), a value obtained by multiplying a prescribed width (W1) by the random coefficient (±). The control device calculates control limit lines (L1, L2) based on the rotation speed of the motor, and corrects the random frequency (fr) so as to fall within a range that is higher than the control limit line (L1) and lower than the control limit line (L2). The control device generates a carrier signal (CR) having a random frequency (fr) as a carrier frequency.