In battery voltage monitoring ICs for measuring voltages of unit cells of an assembled battery, communication with a system control unit is realized in consideration of fail-safe. The system control unit and the battery voltage monitoring ICs are coupled to each other by a communication path using a daisy chain. Each battery voltage monitoring IC has a placement setting pin designating, by a binary code, a unit cell group to which the IC is coupled, in the unit cell groups. When it is detected that the Hamming distance between the code indicative of coupling to a group of the highest potential or a group of the lowest potential and a state actually set in the placement setting pin is 1, some failure such as line disconnection, short-circuit, or the like in the placement setting pins is detected, and the communication path is interrupted.