PURPOSE: To extend the distance of run of an electric car per charge by reducing the waste of battery power through the reduction in the exciting current of an induction motor according to the decrease in the load of the electric car.

CONSTITUTION: An accelerator tread ACC is assumed to be 100% when an electric car drive motor is heavily loaded to develop a high torque, e.g. when the car is being accelerated. A magnetic flux command arithmetic circuit 22 outputs 100% magnetic flux command * according to actual car speeds Nist, input through an absolute value amplifier 21, until the car reaches a specified speed. When the car speed Nist exceeds the specified speed, the circuit 22 gradually lowers the magnetic flux command * to reduce the magnetic flux. This reduces an iron loss at a light load decreasing the waste of battery power, thereby extending the distance of run per charge.