A block comprises physical addresses 0, 1, 2, 3. In an initial state, all the physical addresses 0, 1, 2, 3, are in an erase state. When data LA0, LA1, LA2, LA3 are written in the physical addresses 0, 1, 2, 3, count values are "1", respectively. In this manner, a write/erase operation is performed by a page (physical address) unit, and the count value of the physical address in which the data has been renewed is renewed. Finally, when a total of the count values in the block reaches an allowable value 32, refresh is performed, and states of memory cells in the block are initialized.