PURPOSE: To perform writing sufficiently to the extent that the oscillation of a sense amplifier is prevented at the time of reading by verifying whether writing to a cell transistor is sufficiently executed or not to such an extent that the oscillation of the sense amplifier is prevented at the time of reading.

CONSTITUTION: By incorporating with a write verifying circuit 13, only when the sense amplifier 12 stably outputs 'L' i.e., when writing is sufficiently executed to the extent that the oscillation of the sense amplifier 12 is prevented after writing, the 'L' on the same level as that of writing data DI is outputted as output data DO. When the sense amplifier 12 stably outputs 'H' and oscillates after writing, i.e., when the writing does not performed to the extent that the oscillation of the sense amplifier 12 is prevented, the 'H' on a different level from that of the writing data DI is outputted as the output data D0.