An abnormality of a current sensor or a voltage sensor is detected. An abnormality detecting section reads out a charging/discharging current I of a secondary battery detected by the current sensor and a battery voltage V of the secondary battery, calculates an estimated battery voltage Vs on the basis of an electromotive force E and an internal resistance r of the secondary battery, and judges the current sensor to be abnormal if the difference between the battery voltage V and the estimated battery voltage Vs is greater than a predetermined threshold and the charging/discharging current I exceeds a predetermined allowable range, and judges the voltage sensor to be abnormal if the difference is greater than the predetermined threshold and the charging/discharging current I is within the predetermined allowable range.