In an optical recording and reproducing medium having a groove 2 formed along a recording track and which is recorded and/or reproduced with irradiation of light L having a predetermined wavelength λ, a track pitch p of the groove 2 is selected in a range of from 200 nm to 350 nm and a ratio wg′/p between a width wg of the groove 2 and the track pitch p is selected in a range of from 0.24 to 0.67.