A photodetector and optical pickup device which comprises: a monitoring photodetection element (photodiode) 23 for receiving laser beams having different wavelengths from laser light sources; a light source-discriminating photoreceiver 24 represented by a photodiode (240) and a wavelength selection filter (241) for discriminating the wavelength spectra of the laser light sources; and a sensitivity regulation circuit (25) for regulating the sensitivity of the monitoring photodetection element 23 in response to the light source-discriminating photoreceiver 24.