A flash memory device includes a flash memory and a buffer memory. The flash memory is divided into a main region and a spare region. The buffer memory is a random access memory and has the same structure as the flash memory. In addition, the flash memory device further includes control means for mapping an address of the flash memory applied from a host so as to divide a structure of the buffer memory into a main region and a spare region and for controlling the flash memory and the buffer memory to store data of the buffer memory in the flash memory or to store data of the flash memory in the buffer memory.