A DC voltage on an electric car stringing is supplied to a variable voltage and variable frequency PWM inverter so as to be converted into a three-phase alternating current which is supplied to a plurality of three-phase induction motors. The motors are connected to different wheels to drive an electric car. The inverter is controlled on the basis of an operating frequency command determined by adding or subtracting a slip frequency command to or from a motor speed and a voltage command proportional to the operating frequency command. On the other hand, a motor current command is set and compared with a maximum current value of currents of the plurality of motors, and the slip frequency command is corrected in accordance with a difference therebetween. In a constant torque region of the electric car, a correction value increasing in proportion to the speed is then added to the motor current command, so that torque of motors other than a motor to which the maximum current flows compensates for a decrease in torque caused as the speed increases to improve constant torque characteristics.
