An electrolyte membrane 22 constituting a membrane electrode assembly includes thick portions 23 having a relatively large thickness. The thick portions 23 have a strip shape and are disposed at a predetermined distance from each other along the electric conduction direction. The thick portions 23 extend from one side L1 of the electrolyte membrane 22 extending in a direction perpendicular to the electric conduction direction to the other side L2 of the electrolyte membrane 22 extending in the direction perpendicular to the electric conduction direction. The thick portions 23 have a convex shape with respect to the anode side surface and the cathode side surface of the electrolyte membrane 22.