There is disclosed a memory system including a memory cell array, a sense amplifier circuit, a write circuit, a level setting circuit, a column decoder, a data line, and a sense amplifier control circuit. The level setting circuit sets external input data to substantially the same level as a read potential difference level from the memory cell. The external input data whose level has been set by the level setting circuit is transferred to the sense amplifier selected by the column decoder via the data line. The sense amplifier control circuit activates the selected sense amplifier so as to write the external input data into the memory cell with substantially the same sequence as that at a data read time from the memory cell.