Flip-flop memory cells are connected to a pair of bit lines and respectively to word lines. A word line driver outputs a word line selection pulse to one of the word lines in a word line selection period. A write circuit gives a potential difference corresponding to input data to the pair of bit lines after a start of the word line selection period. In a first operation mode, the potential difference of the pair of bit lines is reset in the word line selection period, and in the second mode, the potential difference of the pair of bit lines is reset after the word line selection period.
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