PURPOSE: To reduce the variation of track detecting sensitivity by performing processing in order to increase the absolute value of a reflectance by formation of a recording pit and also to obtain a prescribed amount of phase variation of the reflectance.

CONSTITUTION: A foundation layer 11 having a higher dielectric constant than a substrate 2 is set at a proper level of thickness. A recording medium consists of the layer 11 and a recording layer 3'. The track detecting sensitivity is deteriorated by the variation of the phase difference owing to formation of a recording pit and also by the deterioration of the reflected light quantity itself with a recording medium having the deterioration of the reflectance at a pit position. Therefore it is possible to prevent the deterioration of the track detecting sensitivity due to the deterioration of the reflected light quantity with a recording medium having an increase of the reflection factor at the pit position. Thus it is possible to obtain a recording medium that produces virtually no change of the track detecting sensitivity by having an optimum form of a groove track as long as the phase difference of the reflectance owing to formation of a recording pit is set at Δ<90° and the recording pit is equal to a reflectance increasing type pit.