One embodiment of the disclosure includes an A-D conversion circuit connected to a photodiode for providing a silicon photomultiplier that with enhanced detection accuracy and a time resolution. A current generated upon photon detection by the photodiode partially flows into another photodiode adjacent to the photodiode arranged in parallel via a resistor. At this time, the current is charged into a parasitic capacitance adjacent to the photodiode, and thereafter is discharged. However, the discharged current cannot flow toward an output terminal by the A-D conversion circuit, and also cannot switch the A-D conversion circuit. Consequently, the construction of the disclosure can detect light with no influence of the current discharged from the parasitic capacitance. As a result, the disclosure achieves a silicon photomultiplier with high detection accuracy and a satisfactory time resolution.