A battery pack includes electric cells connected in series or in parallel between first and second lines, each of the electric cells having a battery cell, a control circuit which performs authentication processing, a communication block which is connected to the control circuit and superimposes a series binary data string on a battery output of the battery cell, and a switching element controlled by the control circuit. The control circuit generates its address. The control circuit of each electric cell transmits the series binary data string including the address to a main body via the communication block and the first and second lines for authentication on each electric cell. The switching element is turned on when the authentication is successful, and charging or discharging is performed. The switching element is turned off when the authentication is unsuccessful, and charging or discharging is banned.