PURPOSE: To enable recording and reproducing of optical information using recording marks smaller than the wavelength of the light source.

CONSTITUTION: A slider 18 provided with an optical head 15 on one side of the optical information recording medium 30 and with a reflector on the other side of the medium 30 is disposed. The recording light emitted from the optical head 15 penetrates the medium 30, and is partly reflected with the reflector to re-enter the medium 30 and form a recording mark there. The reproduction light emitted from the optical head 15 penetrates the medium 30 and is partially reflected to penetrate the medium 30 again and be received by the optical head 15. By this process, the recording mark in the medium 30 is read out. Therefore recording marks smaller than the wavelength of the light source are formed to allow recording and reproducing information accompanied by improved crosstalk.