PURPOSE: To attain the accumulation of high density by setting a precharge potential with respect to a bit line to be a half of a power voltage only by means of bit line vs.potential equalization which is executed at the beginning of device activation even if the storage device is affected with power voltage fluctuation in the middle of standby.

CONSTITUTION: At the time of T0 when the storage device stands by, a selection signal 2 and a raw selection signals WL are in low states. On the other hand, a precharge signal R is low, a sensitive amplifier driving signal 1N is high, a signal 1P is low, and the sensitive amplifier is activated. Either of a BL with respect to bit line and a BL is equalized by the power source, and the other is connected with an earth point, whereby they are charged to respective potentials. Even if power voltage fluctuation occurs at the time of standing by, one of the potentials with respect to the bit line goes to the power voltage VCC and the other to an earth potential. When the storage device is activated at the time of T1, the signal 1N is set low, and the signal 1N to high, whereby the sensitive amplifier is once stopped. The potential of the signal R at the time of T2 is set to VCC/2 at the time of device activation, and the precharge of the bit line is terminated.