A malfunction detecting apparatus for detecting a malfunction of a voltage detecting device accurately, including a low-voltage-system CPU which controls voltage detecting circuits to detect voltage between both terminals of one unit cell from among unit cells included in blocks corresponding to voltage detecting circuits. When variation of the voltage between both terminals detecting by the low-voltage-system CPU is at least an allowable error determined by a detection accuracy of the voltage detecting circuits, an abnormal condition of the voltage detecting circuits is detected.