Memory device and method for controlling memory device

Provided is a memory device with improved memory region usage efficiency. The memory device includes flash memory including: a control information (FAT) region that stores FAT for a file and a user data (UD) region that stores UD; cache memory including a FAT cache region that stores all or part of the FAT; an I/F that receives a write command for writing one of the FAT and the UD; and a memory controller that determines whether write data to be written is the FAT or the UD based on an address included in the write command, and sets the size of the FAT cache region based on an update frequency or an update count for the address included in the write command for the write data determined to be the FAT by the determiner.