To provide a charge/discharge controller having a simple arrangement at a low cost.

A plurality of unit capacitors are connected in series as cells C1-C5 to constitute a power supply pack. Bi-directional switches S1-S23 are arranged between respective cells including the outer terminals of the cells C1 and C5. Each bi-directional switch is connected, at one end thereof, with the outer terminals of the cells C1 and C5 and the connection end between respective cells and, at the other end thereof, with connection terminals C and D alternately. Four bi-directional switches S1-S2' are connected, in cross, between the connection terminals C and D and the opposite ends E and F of regulation cells Cx. Under control of a first switch control circuit 10 and a second switch control circuit 12A, the regulation cells Cx are connected sequentially with respective cells of the power supply pack. Voltages of respective cells are made uniform through charge/discharge between the regulation cells Cx and respective cells thus preventing over discharge and overcharge due to variation of cell capacity. Since the charge/discharge controller is constituted of bi-directional switches and a simple control circuit, the cost can be reduced.