A connection mode of a plurality of arbitrarily connected storage units is detected and the plurality of storage units is controlled according to the detected connection mode.Six storage modules MOD1 to MOD6 are connected in series. A total voltage V(Total) and individual output voltages V(1) to V(6) of respective storage modules are supplied to an output controller ICNT. A controller PR of the output controller ICNT determines the connection mode depending on whether a determination equation is satisfied. When the number of storage modules is set to N, the total output voltage is set to V(Total), the individual output voltages are set to V(1), V(2), . . . , and V(N), and the number of parallels of the connection mode is set to M, (determination equation: V(1)=V(2)= . . . =V(N)=(1/M)×V(Total)) is used. When the determination equation is satisfied, (N/M) parallel M series is determined.