A digital still camera performs temporary high-speed writing when capturing a large number of images in a short time. Lengthy processing for erased block allocation or copying performed inside a nonvolatile storage device may disable the captured images to be written completely (may cause some frames to drop). A nonvolatile storage system includes an access device (1001) and a nonvolatile storage device (1002). A button operation of a user on the access device (1001) causes the mode of data writing to the nonvolatile storage device (1002) to be switched. Temporary high-speed writing is performed into a physical block of a nonvolatile memory (27) from which a plurality of data pieces with different logical addresses and different data sizes have been erased. After the temporary high-speed writing, the written data is relocated into a user storage area (272), and an erased block is newly allocated for subsequent temporary high-speed data writing.