A light detecting apparatus includes: a first photoelectric conversion element unit (110) and a second photoelectric conversion element unit(120) each of which converts input light to an electric current and output it； an optical current transducer unit (100) for outputting, as a detected current, a differential current between an electric current outputted by the first photoelectric conversion element unit and an electric current outputted by the second photoelectric conversion element unit； and a first current/voltage converting unit (200) for amplifying the detected current outputted from the optical current transducer unit, converting it to a voltage signal, and outputting the voltage signal.
