PURPOSE: To unnecessitate to open-circuit the disconnecting switch and the like of the titled device by a method wherein, when coasting a vehicle having an induction motor to be driven by a variable voltage and a variable frequency inverter, the torque of motor is brought into zero by making a slip frequency zero.

CONSTITUTION: The induction motor 9 is driven through the intermediary of a variable voltage and a variable frequency inverter 8, and a power running, a regenerated control and a coasting driving of the electric vehicle are performed. At this time, the torque pattern T required for the electric vehicle is inputted to a function generator 10, and the slip frequency fS which will be determined by said function generator 10 is outputted. Also, the number of revolution fr of the motor 9 is outputted by inputting the number of revolution R of the motor 9 to a converter 12, and the output frequency fI of the inverter 8 is commanded by performing an arithmetic operation using an arithmetic unit 16. Accordingly, the torque of the motor can be zeroed by zeroing a slip frequency fS without open- circuiting a disconnecting switch and the like when the vehicle is coasting, thereby enabling to drive the vehicle smoothly.