PURPOSE: To improve efficiency for performing access to each track on a data disk by providing an attached information track for writing attached information in a data disk part on outside rather than a data track.

CONSTITUTION: The attached information are recorded to an attached information track 12 formed in the outside part rather than a data track 11 of each data disk 1. For the selection of this track 12 and the positioning control of a head after the track selection, OGB (outer guard bands) 24-26 and a servo track 22 for attached information track are formed in a part outside to the area of a servo track 21 for data track in a servo disk 2. Thus, since an attached information write area is provided near an O cylinder as the home position of the head, time is shortened for performing access to this area when a power source is turned on so that a frequency for a host device to require these attached information can be made high.