PURPOSE: To make automatic processig possible at the time of abnormal recovery by recording dummy data.
CONSTITUTION: To read control part 3, comparator circuit part 5 and dummy address recording part 7 are connected in sequence and between comparator circuit part 5 and dummy address memory part 7, write control part 4 is connected. As a result, when addresses fo address memory part 6 are updated, dummy data address memory part 7 is stored those updated addresses and write control part 4 refers to addresses in address memory part 6 by a write request signal from transmission- reception control part 8 to controller 2. In case that when transmitted data are written at a corresponding address position on floppy disk 1, the previous write position is lost due to the occurrence of abnormality such as power break, data read from floppy disk 1 by read control part 3 is compared by comparator circuit part 5 with dummy data in dummy data memory part 7. Then, addresses of write address part 6 are read out being updated until the both agree each other and the next process starts automatically from a coincidence point.