A photodetector device comprising: an avalanche photodiode array substrate in which a plurality of avalanche photodiodes arranged to operate in a Geiger mode are two-dimensionally arranged, the avalanche photodiode array substrate being formed from compound semiconductor; and a circuit substrate on which the avalanche photodiode array substrate is mounted, wherein the circuit substrate includes a plurality of output units connected to each other in parallel to form at least one channel, each of the output units includes a passive quenching element connected in series to at least one of the plurality of avalanche photodiodes, and a capacitative element connected in series to at least one of the avalanche photodiodes and connected in parallel to the passive quenching element, and either: the passive quenching element is formed by a first polysilicon layer provided in the circuit substrate, the capacitative element is formed by a second polysilicon layer provided in the circuit substrate, a dielectric layer stacked on the second polysilicon layer, and a third polysilicon layer stacked on the dielectric layer, and the first polysilicon layer is formed at the same height as in the second polysilicon layer or the third polysilicon layer in a thickness direction of the circuit substrate, or the passive quenching element is formed by a metal thin film provided in the circuit substrate, the capacitative element is formed by a first metal layer provided in the circuit substrate, a dielectric layer stacked on the first metal layer, and a second metal layer stacked on the dielectric layer, and the metal thin film is formed at the same height as in the first metal layer or the second metal layer in a thickness direction of the circuit substrate. an avalanche photodiode array substrate in which a plurality of avalanche photodiodes arranged to operate in a Geiger mode are two-dimensionally arranged, the avalanche photodiode array substrate being formed from compound semiconductor; and a circuit substrate on which the avalanche photodiode array substrate is mounted, wherein the circuit substrate includes a plurality of output units connected to each other in parallel to form at least one channel, each of the output units includes a passive quenching element connected in series to at least one of the plurality of avalanche photodiodes, and a capacitative element connected in series to at least one of the avalanche photodiodes and connected in parallel to the passive quenching element, and either: the passive quenching element is formed by a first polysilicon layer provided in the circuit substrate, the capacitative element is formed by a second polysilicon layer provided in the circuit substrate, a dielectric layer stacked on the second polysilicon layer, and a third polysilicon layer stacked on the dielectric layer, and the first polysilicon layer is formed at the same height as in the second polysilicon layer or the third polysilicon layer in a thickness direction of the circuit substrate, the passive quenching element is formed by a first polysilicon layer provided in the circuit substrate, the capacitative element is formed by a second polysilicon layer provided in the circuit substrate, a dielectric layer stacked on the second polysilicon layer, and a third polysilicon layer stacked on the dielectric layer, and the first polysilicon layer is formed at the same height as in the second polysilicon layer or the third polysilicon layer in a thickness direction of the circuit substrate, or the passive quenching element is formed by a metal thin film provided in the circuit substrate, the capacitative element is formed by a first metal layer provided in the circuit substrate, a dielectric layer stacked on the first metal layer, and a second metal layer stacked on the dielectric layer, and the metal thin film is formed at the same height as in the first metal layer or the second metal layer in a thickness direction of the circuit substrate. the passive quenching element is formed by a metal thin film provided in the circuit substrate, the capacitative element is formed by a first metal layer provided in the circuit substrate, a dielectric layer stacked on the first metal layer, and a second metal layer stacked on the dielectric layer, and the metal thin film is formed at the same height as in the first metal layer or the second metal layer in a thickness direction of the circuit substrate.