Abstract: A signal processing circuit configured with a superconducting digital logic circuit and used for processing detection signals output from superconducting single photon detectors (SSPDs) includes transmission paths connected to the SSPDs on a one-to-one basis, a branching unit causing each of the transmission paths to branch into a first transmission path and a second transmission path, a time information generation circuit connected to the first transmission paths, and an address information generation circuit connected to the second transmission paths. The time information generation circuit outputs, based on the detection signals output from the SSPDs, a time information signal for identifying a time at which a photon is incident on the SSPDs, and the address information generation circuit outputs, based on the detection signals output from the SSPDs, an address information signal for identifying an SSPD on which a photon is incident from among the SSPDs.