A membrane electrode assembly, comprising: a polymer electrolyte membrane; and an electrode catalyst layer bonded to the polymer electrolyte membrane, the layer comprising: a catalyst substance; a conductive carrier; a polymer electrolyte; and a fibrous substance, wherein the conductive carrier has conductivity and carries the catalyst substance without being affected by the catalyst substance, wherein the axes of the fibrous substance are not aligned in only one direction, the amount of the fibrous substance in which inclination θ of axes with respect to a surface of the electrode catalyst layer bonded to a surface of the polymer electrolyte membrane is 0° ≤ θ < 40°, among the fibrous substance, is greater than 80% of the total amount of the fibrous substance contained, and the amount of the fibrous substance in which inclination θ of the axes of the fibrous substances is 0° ≤ θ < 20° is less than 70% of the total amount of the fibrous substance contained; wherein the inclination θ of axes is measured as detailed in the specification; wherein the fiber diameter of the fibrous substance is from 0.5 to 500 nm, and the fiber length of the fibrous substance is 1 to 40 μm; and wherein a thickness of the electrode catalyst layer is 5 μm to 30 μm. a polymer electrolyte membrane; and an electrode catalyst layer bonded to the polymer electrolyte membrane, the layer comprising: a catalyst substance; a conductive carrier; a polymer electrolyte; and a fibrous substance, wherein the conductive carrier has conductivity and carries the catalyst substance without being affected by the catalyst substance, wherein the axes of the fibrous substance are not aligned in only one direction, the amount of the fibrous substance in which inclination θ of axes with respect to a surface of the electrode catalyst layer bonded to a surface of the polymer electrolyte membrane is 0° ≤ θ < 40°, among the fibrous substance, is greater than 80% of the total amount of the fibrous substance contained, and the amount of the fibrous substance in which inclination θ of the axes of the fibrous substances is 0° ≤ θ < 20° is less than 70% of the total amount of the fibrous substance contained; wherein the inclination θ of axes is measured as detailed in the specification; wherein the fiber diameter of the fibrous substance is from 0.5 to 500 nm, and the fiber length of the fibrous substance is 1 to 40 μm; and wherein a thickness of the electrode catalyst layer is 5 μm to 30 μm. a catalyst substance; a conductive carrier; a polymer electrolyte; and a fibrous substance, wherein the conductive carrier has conductivity and carries the catalyst substance without being affected by the catalyst substance, wherein the axes of the fibrous substance are not aligned in only one direction, the amount of the fibrous substance in which inclination θ of axes with respect to a surface of the electrode catalyst layer bonded to a surface of the polymer electrolyte membrane is 0° ≤ θ < 40°, among the fibrous substance, is greater than 80% of the total amount of the fibrous substance contained, and the amount of the fibrous substance in which inclination θ of the axes of the fibrous substances is 0° ≤ θ < 20° is less than 70% of the total amount of the fibrous substance contained; wherein the inclination θ of axes is measured as detailed in the specification; wherein the fiber diameter of the fibrous substance is from 0.5 to 500 nm, and the fiber length of the fibrous substance is 1 to 40 μm; and wherein a thickness of the electrode catalyst layer is 5 μm to 30 μm.