ELECTRODE CATALYST FOR FUEL CELL, ELECTRODE CATALYST LAYER FOR FUEL CELL, MEMBRANE/ELECTRODE ASSEMBLY, AND FUEL CELL

An electrode catalyst for a fuel battery includes a mesoporous material and catalyst metal particles supported at least in the mesoporous material. In the electrode catalyst for a fuel battery, before supporting the catalyst metal particles, the mesoporous material has mesopores having a mode radius of greater than or equal to 1 nm and less than or equal to 25 nm and has a value of greater than 0.90, the value being determined by dividing a specific surface area S1-25 (m2/g) of the mesopores obtained by analyzing a nitrogen adsorption-desorption isotherm according to a BJH method, the mesopores having a radius of greater than or equal to 1 nm and less than or equal to 25 nm, by a BET specific surface area (m2/g) evaluated according to a BET method.