An optical pickup equipped with a laser light source which emits light beams of at least three wavelengths for recording/reproducing a plurality of information recording media detects light quantities of the light beams of three wavelengths using one light intensity monitor element. More specifically, one light intensity monitor element is arranged between a first laser light source and a second laser light source, light beams of wavelength λ1 and wavelength λ2 emitted from the first laser light source are made to proceed substantially straightforward, the optical path of the light beam of wavelength λ3 emitted from the second laser light source is changed to a diagonal one so as to cause the light beam to be introduced diagonally to the light receiving surface of the one light intensity monitor element. Furthermore, the central axis line of the light receiving surface of the one light intensity monitor element is separated from the emitted light axis of the first laser light source and a reflecting member is provided above the emitting light axis of the second laser light source.