A controller in the electric vehicle is provided in which data which are criteria to determine a magnitude of degradation tendency of a high-voltage secondary cell are stored in a ROM in a high-voltage battery electrical controller. When it is detected that an ignition switch is turned off, the magnitude of the degradation tendency is determined depending on a temperature of the high-voltage secondary cell and a state of charge value based on the data. When it is determined that the degradation tendency is large, the battery fan and the air conditioner are operated so that the state of charge value and the temperature decrease. Next, while repeating determination of the magnitude of the degradation tendency, when it is determined that the degradation tendency is small, the operation of the battery fan and the air conditioner is stopped. Therefore, the state of charge value is prevented from decreasing more than necessary.