A proton conductor includes an electrolytic layer having first and second main surfaces; and a plurality of catalyst particles. The first main surface of the electrolytic layer includes a flat portion and a plurality of recessed portions. The plurality of catalyst particles are respectively located in the plurality of recessed portions. The flat portion of the first main surface and parts of surfaces of the plurality of catalyst particles exposed from the plurality of recessed portions form a third main surface. The electrolytic layer is formed of a single crystal of a perovskite-type oxide having a proton conductivity. The catalyst particles are formed of a single crystal of a noble metal material. The perovskite-type oxide of the electrolytic layer) has a crystal orientation that matches a crystal orientation of the noble metal material of the plurality of catalyst particles.