The present invention aims at providing a photodetector which can detect the incident light intensity with a high speed while having a wide dynamic range for incident light intensity detection. Each photodiode PDm,n generates electric charges Q by an amount corresponding to the intensity of light incident thereon. An electric charge amount level determining circuit 10m,n is provided so as to correspond to the photodiode PDm,n, determines the level of the amount of electric charges Q generated by the photodiode PDm,n, and outputs a level signal Level indicative of the result of level determination. The capacitance value of the integral capacitance part 21 in the integrating circuit 20m is set by the respective level signals Level sequentially fed from N electric charge amount level determining circuits 10m,1 to 10m,N. The integrating circuit 20m accumulates the electric charges Q fed to the input terminal sequentially from the N electric charge amount level determining circuits 10m,1 to 10m,N into the integral capacitance part 21, and outputs a voltage V20 corresponding to the amount of thus accumulated electric charges Q from the output terminal.