To prevent the traveling performance of an electric vehicle, having a brushless DC motor as its driving power source, from being lowered by the increase of a load when an economical operation mode is selected.

Information concerning a traveling speed of a vehicle is obtained from changes in outputs Hu-Hw of position sensors hu-hw provided on a brushless DC motor 1. Data showing relations between the driving currents Iu-Iw of the motor 1 and the traveling speed of the vehicle while a load of the motor is equal to a set value are stored in a ROM of a microcomputer as a traveling time load deciding map. It is decided whether the load of the motor exceeds the set value or not by using the detected driving currents, the traveling speed, and the traveling time load deciding map. If it is decided that the load applied to the motor exceeds the set value when an economical operation mode is selected, the operation mode is switched to a normal operation mode.