According to this invention, when initialization of a storage medium such as a flash memory is erase of the data area, the processing can be stopped. When the processing is stopped, at least initialization of the management area has been completed, and processing using the storage medium can be executed. If erase processing is not stopped but proceeds to the end, no erase processing need be performed in writing new data, and high-speed write is promised. For this purpose, when complete formatting is designated, the management area of the file system is first initialized. Then, erase processing for the data area of the file system is executed by a predetermined block size. If it is determined that stop is designated during the data area erase processing, the processing ends, but the management area has already been initialized.