A magnetic recording and reproducing device includes: a magnetic recording medium in which a magnetic recording layer is formed in a concavo-convex pattern so that tracks are formed by convex portions of a predetermined track width and arranged in parallel in the track width direction; a heating head for heating the magnetic recording medium to partially reduce coercivity of the tracks; a recording head for applying a recording magnetic field to a heated portion of the magnetic recording medium to record magnetic data on the tracks; and a reproducing head for detecting a reproducing magnetic field of the tracks. In this configuration, an effective recording area has an effective recording width that is equal to or more than the track width, and equal to or less than a sum of the track width and a doubled value of width of concave portions between the tracks.