Provided is a proton conductor that achieves an improvement in transport number while suppressing a decrease in conductivity. The proton conductor contains a metal oxide having a perovskite structure and represented by formula (1): AaB1-x-yB′xMyO3-δ (1), wherein an element A is at least one element selected from the group consisting of Ba, Sr, and Ca, an element B is at least one element selected from the group consisting of Zr and Ce, an element B′ is Hf, an element M is at least one element selected from the group consisting of Y, Yb, Er, Ho, Tm, Gd, In, and Sc, δ is an oxygen deficiency amount, and “a”, “x”, and “y” satisfy 0.9≤a≤1.0, 0.1≤y≤0.2, and 0