We propose and demonstrate a low-power and low-current cryogenic readout interface for a superconducting nanowire single-photon detector (SSPD) using adiabatic quantum-flux-parametron (AQFP) logic. The AQFP readout interface samples and digitizes the current signal from an SSPD, generating binary output data in accordance with the detection behavior of the SSPD. We demonstrate the correct operation of an SSPD with the interface, where the AQFP readout interface and the SSPD are placed in separate 0.1-W Gifford–McMahon (GM) cryocoolers and are interconnected via coaxial cables. It was found that the temperature of the sample stage did not change even after the AQFP readout interface was turned on, which revealed that the AQFP readout interface uses sufficiently low power and current for a compact cryocooler.