To stably maintain the emitted light intensity of a light source and also to obtain superior reproduced signals by making the polarization direction of the light from the light source orthogonally cross that of the return light when the return light from a light probe side generating a minute spot is made incident on the light source.

With a polarization converting element 8, the polarization direction of the light emitted from the light source 4 is controlled to orthogonally cross that of the return light which is reflected by a recording medium 1 and which returns to the light source 4 side through the optical probe 7. Consequently, interference of light inside the light source 4 is reduced, so that the light returning from the recording medium 1 to the light source 4 passes through without hardly affecting the emitted light intensity of the light source 4. Accordingly, the emitted light intensity of the light source 4 is stably maintained and, the light passing through this light source 4 is received by a photodetector 9 arranged in the rear side of the light source 4, thereby obtaing satisfactory reproducing signals.