Abstract: A photodetector device includes an avalanche photodiode array substrate formed from compound semiconductor. A plurality of avalanche photodiodes arranged to operate in a Geiger mode are two-dimensionally arranged on the avalanche photodiode array substrate. A circuit substrate includes a plurality of output units which are connected to each other in parallel to form at least one channel. Each of the output units includes a passive quenching element and a capacitative element. The passive quenching element is connected in series to at least one of the plurality of avalanche photodiodes. The capacitative element is connected in series to at least one of the avalanche photodiodes and is connected in parallel to the passive quenching element.