To provide a photo detection circuit that cancels a nonlinear characteristic caused by a leakage current in a low photoreceiving level of a photodiode for detecting input light to be detected.

This circuit is provided with a photodiode 2 having a characteristic equal to that of the photodiode 1 input with a signal of the detected input light. An output current is subtracted by a subtraction circuit 7 using currents of the photodiodes 1, 2 respectively as input currents for current mirror circuits 4, 5, then smoothed by a smoothing circuit 8, and input to a comparator 9, so as to cancel, thereby, the influence of the leakage current in the photodiode 1 effectively.