PURPOSE: To enable to know the residual recording capacity of track in a short time, by fetching the information representing the residual track length in the record recorded on track and making effective use of the magnetic disc.

CONSTITUTION: Although the start point 2 and end point 3 of track are actually at the same location because the track forms a loop, a plurality of recording areas are provided between the points. The record (n) consists of the field 4 of length A and the field 5 of length B, and the gap 6 of length C is provided between the fields 4 and 5. The field 4 consists of the address section 7 of the fixed length A and showing the address of the record (n), display section 8 showing the length of the field 5, and residual capacity display section 9 showing the length from the back end of the field 4 to the end point 3 of track, and the length B of the field 5 is of variable length and the data is recorded.