Provided is a light detecting device including: a light path branching unit that branches a single detection light path of fluorescence from a specimen, into a plurality of branched light paths; a plurality of light detectors that are provided to the respective branched light paths branched by the light path branching unit and that include an SSPD or Geiger mode APD to detect the fluorescence; and a signal adder that generates a single image signal in accordance with the detection signals outputted from the plurality of light detectors.