PURPOSE: To set the initial output value of a battery mounted on an electric vehicle to a rational and proper value.

CONSTITUTION: The initial output Pmaxi of a battery is set to the output of not less than an output in which the output decrease Pm of a secondary battery due to its memory effect and the allowable output decrease Pcn of the secondary battery due to its deterioration with time are added to the set output Pl of a motor. Namely, since the set output Pl of the motor is determined in anticipation of the decrease due to the memory effect and the deterioration with time, even when the decrease and the deterioration are generated, a minimum output Pl which the secondary battery has as real power is not decreased below the set output Pl at the prescribed number of times of charge and discharge within t=n times. Accordingly, an effect is achieved that makes a driver who is a user become unaware of the deterioration of power performance due to the output decrease of the battery, in other words, the decrease of the set output Pl of the motor.