The membrane electrode assembly 1 has an anode 10, a cathode 20, and an electrolyte membrane 30 disposed between the anode and cathode; the anode and cathode are gas diffusion electrodes; the electrolyte membrane contains a solid electrolyte in which a plurality of pores with mean pore diameters of 1 to 30 nm are formed; and the solid electrolyte has a backbone comprising organic groups having one or more metal atoms, oxygen atoms bonded to the metal atoms, and carbon atoms bonded to the metal atoms or oxygen atoms, and also has functional groups with ion-exchange capabilities that are bonded to the organic groups in the pores.