TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Compound: The conductive fiber is carbon fiber. Preferred Properties: The carbon fiber has average fiber diameter of 50-300 nm and mean fiber diameter length of 5-30 mu m.    TECHNOLOGY FOCUS - POLYMERS - Preferred Layer: The cathode and anode further has a gas diffusion layer. The sheet-like reinforcing material has pores. Preferred Material: The sheet-like reinforcing material is nonwoven fabric containing polypropylene or fluorine-containing polymer obtained by melt-blown method, or porous film containing polytetrafluoroethylene. Preferred Arrangement: The reinforcement layer is provided between the catalyst layer and the gas diffusion layer. The reinforcement layer is touched, and further has an intermediate layer. The membrane electrode assembly further has a frame shaped sub-gasket provided at peripheral portion of the membrane electrode assembly of polymer electrolyte fuel cell. Preferred Composition: The reinforcement layer contains a binder. The solid polymer electrolyte membrane contains polymer having a sulfonyl group-containing repeating unit of formula (I) or a fluorine-containing repeating unit: -CF2-C((CF2)tOCF2-CFY2-Q3-SO2X2(SO2R")b-H+)F-.Q1=perfluoro alkylene optionally having ether property oxygen;Q2,Q3=single bond or perfluoro alkylene optionally having ether property oxygen;R',R"=perfluoroalkyl optionally having ether property oxygen;X1,X2=oxygen, nitrogen or carbon;Y1,Y2=fluorine or monovalent perfluoro organic group;ands,t=0 or 1.When X1 is oxygen, a is 0. When X1 is nitrogen, a is 1. When X1 is carbon, a is 2. When X2 is oxygen, b is 0. When X2 is nitrogen, b is 1. When X2 is carbon, b is 2. Preferred Compound: The binder is fluorine-containing ion exchange resin. Preferred Properties: The mass ratio of conductive fiber and binder is 1/0.05-1/1. The sheet-like reinforcing material has mean pore diameter of 0.4-7 mu m and average fiber diameter of 0.2-7 mu m. The solid polymer electrolyte membrane has thickness of 10-30 mu m and equivalent weight of 900 g/equivalent or less. The 90 degrees -pealing strength of interfaces which exist between solid polymer electrolyte membrane and reinforcement layer is 0.5 N/cm or more.