A solid-state image sensor capable of detecting a photon and having smaller circuit scale is provided. The solid-state image sensor includes a pixel array including a plurality of pixel cells, a pixel driving circuit configured to drive the plurality of pixel cells, a readout circuit, and a plurality of readout wires corresponding to respective columns of the pixel cell. Each of the plurality of pixel cells includes an avalanche photodiode configured to detect a photon by avalanche multiplication occurring when one photon enters, and a transfer transistor configured to transfer a detection result of the photon to the corresponding readout wire. The readout circuit determines whether a photon is detected or not, and outputs a determination result.