The magnetic recording and reproducing device has a magnetic recording medium, a recording head for writing magnetic data on the magnetic recording medium, and a reproducing head for reading magnetic data from the magnetic recording medium. In the magnetic recording medium, each track is formed by a convex portion with a predetermined track width, and a plurality of the tracks are arranged in parallel at intervals of a predetermined track gap. The relationship represented by the following formula (I) is satisfied: {Tw+(2.times.Tg)}/1.2.gtoreq.MWw (I) wherein Tw represents the track width, Tg represents the track gap, and MWw represents the magnetic write width of the recording head.