A photodetector receiving object light and ambient light as incident light includes: a sensor circuit in which a sensor outputting a first current corresponding to the intensity of the incident light and a sub-sensor outputting a second current corresponding to the intensity of the ambient light are electrically connected in series with each other via a node; and a differential current detection circuit detecting a differential current between the first current and the second current, which is output from the node at the time of applying a voltage across the sensor circuit. Here, when the voltage applied across the sensor circuit is defined as a first voltage and the voltage output from the node is defined as a second voltage, the intensity of the object light is detected on the basis of the differential current created when the second voltage becomes equal to a reference voltage.