PURPOSE: To shorten a write time by providing plural serial registers for writing data in a memory array.

CONSTITUTION: After data is inputted to a serial input/output register 2, the data is inputted to the serial input/output register 4 while data write is performed from the register 2 to the memory array 6, and thereafter, while the data is read out from the array 6 to the register 2 for verify, the data is written in the array 6 from the register 4. Then, the write time in the array 6 is shortened, and the write and the read of the data are performed simultaneously.