The invention provides a data storage device and a method of updating management information, capable of dealing with management information in a highly reliable manner so that information is not easily lost when an error occurs. File management information such as a FAT serving as address management information in a flash memory is stored in a management information area of the memory, a pair of blocks is assigned as blocks for use to store data of the FAT, and writing of updated FAT information is performed by alternately using the two blocks of the block pair such that previous FAT information is retained in one of the two blocks of the block pair, and updated FAT information is written in the other block of the block pair, whereby, even when an error occurs in the middle of the process of writing the updated management information, a process using the retained previous FAT information is possible.