To provide an optical head capable of enhancing the accuracy of an APC (Auto Power Control) and to provide an optical recording/reproducing apparatus.

A light beam emitted from a light source 1 is made incident on a polarizer 14. If a transmission axis direction of the polarizer 14 is previously adjusted so that P polarized light is transmitted, only the light quantity of S polarized light can be reduced. The light beam transmitted through a diffraction element 2 and a collimator lens 3 and made incident on a beam splitter 4a is an almost all P polarized light. A portion of the light beam reflected on the beam splitter 4a is made incident on a light detector 13 and used for feedback control of output of the light source 1. Since the light quantity of the S polarized light is reduced by the polarizer 14, only the P polarized light is made incident on the light detector 13. Thereby, the ratio of light quantity of light for recording and reproduction to light quantity of light for APC is made nearly constant even when emission light quantity of a laser beam is changed, detection accuracy of intensity of the laser beam can be enhanced and error in recording and reproduction can be avoided.