Memory cell write/read method and page buffer using write code and read code which is different from the write code

A memory cell write/read method and page buffer is provided to use respective optimized code at writing operation and read operation by using the different code in the writing operation and read operation. In a writing / read method of the memory cell having a plurality of threshold voltage distributions, n-bit data is written in the memory cell by using a writing code indicating corresponding threshold voltage distribution among a plurality of threshold voltage distributions. N-bit data is read from the memory cell by using a reading code indicating corresponding threshold voltage distribution among a plurality of threshold voltage distributions.