A semiconductor integrated circuit device is disclosed. The device includes a memory cell array, an I/O buffer, a read/write buffer, an error checking and correcting circuit, and an initialization checking circuit. N-bit data is input to the I/O buffer and the I/O buffer outputs N-bit data. The I/O buffer inputs N-bit data to the read/write buffer, and the read/write buffer outputs N-bit data to the I/O buffer. The memory cell array inputs up to M×N-bit data to the read/write buffer, and the read/write buffer outputs up to M×N-bit data to the memory cell array. The read/write buffer writes a variable number of bits to the memory cell array (N is a natural number equal to or larger than 1, and M is a natural number equal to or larger than 2).