A magnetic storage medium has tracks and guard bands magnetically separating adjacent tracks. The tracks and the guard bands are alternately and concentrically disposed. The tracks includes a plurality of data tracks in which data can be written and from which data can be reproduced and servo patterns disposed between the data tracks and allowing reproduction of positional information of the data tracks. The magnetic storage medium includes an offset-amount measurement area in which traverse tracks are formed so as to traverse adjacent tracks via each of the guard bands so that writing regarding offset measurement data for measuring an offset amount between a storage element and a reproducing element of a magnetic head unit is allowed at a center position of the storage element.