The membrane-electrode-assembly of the present invention has a polymer electrolyte membrane, a pair of catalyst layers opposed to each other to interpose the polymer electrolyte membrane therebetween, and an anode gas diffusion layer and a cathode gas diffusion layer opposed to each other to interpose the polymer electrolyte membrane and the paired catalyst layers therebetween, wherein a porosity of the anode gas diffusion layer is 60% or less, a porosity of the cathode gas diffusion layer is larger than that of the anode gas diffusion layer, and the anode gas diffusion layer is made of a porous member mainly including conductive particles and a polymeric resin. In this manner, the power generating performance is further improved.