The objective of the invention is to increase gas diffusibility while increasing proton transportability, in a catalyst layer of a membrane electrode assembly. This membrane electrode assembly contains an electrolyte membrane and a pair of electrode layers disposed so as to sandwich the electrolyte membrane, the pair of electrode layers comprising a pair of catalyst layers disposed so as to sandwich the electrolyte membrane, and a pair of gas diffusion layers disposed respectively on the sides of the pair of catalyst layers opposite the electrolyte membrane. Among the pair of catalyst layers, at least one catalyst layer comprises a fiber-shaped electric conductor, a catalyst particle, a particle-shaped electric conductor, and a proton conducting resin. In addition, at least one of the catalyst layers comprises a first region whereof the distance from the fiber-shaped electric conductor is 200 nm or shorter, and a second region other than the first region. Holes are present in the first region and the second region, the hole diameter mode M1 in the first region and the hole diameter mode M2 in the second region fulfilling M1 < M2.