To provide a new playback method by which high density development is realized by giving multivalued information to one recording mark and compatibility with the playback system of a conventional CD system and a conventional DVD system is maintained.

With respect to an optical recording medium 6 on which recording marks 10 are formed by (i×j) pieces of mark kinds based on the combination of i-piece length kinds and j-piece height kinds, the length of each recording mark 10 is discriminated by using a general photodetector 7 having light-receiving areas (a) to (d) divided into four on the basis of the addition signals a+b+c+d of all the light-receiving areas divided into four. The height of each recording mark 10 is discriminated on the basis of the subtraction signal (a+d)-(b+c) of the addition signal of the light-receiving areas (a) and (d) present in one side to a direction orthogonal to a recording mark column direction in the light-receiving areas divided into four and the addition signal of the light-receiving areas (b) and (c) present in the other side. Thereby, the compatibility with the playback system of the conventional CD system and the conventional DVD system is maintained about a discrimination method of length.