Abstract: The invention provides a file system for a flash memory which is prevented from becoming disabled suddenly and wherein the time at which the flash memory itself should be exchanged can be estimated. A discrimination circuit discriminates whether or not a re-write occurrence time number of each physical block of the flash memory exceeds a guaranteed re-write time number by which writing can be performed regularly. When the discrimination of the discrimination circuit reveals that the re-write occurrence time number of any one of the physical blocks exceeds the guaranteed re-write time number, a searching circuit searches for a non-used alternate physical block which can be used in place of the one physical block. An alternate physical block production circuit copies described contents of the physical block, with which the re-write occurrence time number exceeds the guaranteed re-write time number, into the alternate physical block.