In a recording/reproducing method of a magnetic tape in a tracking servo system, a recording density of each data track is increased while inhibiting occurrence of a recording/reproducing error caused by a size change of a magnetic tape in the width direction. Data tracks are each set to have a smaller track width stepwise as closer to servo tracks (41T-1 to 41T-5 etc.) in the width direction of a magnetic tape 1. With such a setting, the width of the data tracks (A1-41T-1 to A1-41T-5 etc.) closest to the servo tracks (41T-1 to 41T-5) can be minimized, thereby enabling a significant increase in number of the data tracks. Further, even when the size of the magnetic tape 1 changes in the width direction due to a change in external environment such as a temperature or moisture, to lead to large displacement of the data tracks (A8-41T-1 to A8-41T-5) distant from the servo tracks (41T-1 to 41T-5), the data head (A8) can be readily aligned to face the data tracks (A8-41T-1 to A8-41T-5) in the reproduction by an increased portion of the width size of the data tracks (A8-41T-1 to A8-41T-5), and it is thereby possible to ensure reading of data signals from the data tracks (A8-41T-1 to A8-41T-5) so as to improve reproduction accuracy.