An electrolyte membrane (1) includes a base material layer (1) containing a hydrocarbon-based electrolyte as a main component, and a surface layer (5) laminated with the base material layer (1). The surface layer (5) is a layer containing, as a main component, a polymeric material having a hydroxyl group and a proton conductive group. The polymeric material that constitutes the surface layer (5) contains, for example, a first polymer having a hydroxyl group, and a second polymer having a proton conductive group. A matrix is formed by cross-linking the first polymer, and the second polymer can be held in the matrix.