Disclosed is a fuel cell that contains core-shell catalyst particles in an electrode catalyst layer, and that can maintain the catalytic activity of said core-shell catalyst particles at a high level. The fuel cell-which is provided with a single cell provided with a membrane/electrode assembly provided with: an anode provided with an anode catalyst layer and a gas-diffusion layer on one side of a polymer electrolyte membrane; and a cathode provided with a cathode catalyst layer and a gas-diffusion layer on the other side of the polymer electrolyte membrane-is characterized by the core-shell catalyst particles, which are each provided with a core section and a shell section that covers said core section and that contains a metal shell material, being contained in at least one of either the aforementioned anode catalyst layer or the aforementioned cathode catalyst layer, and by metal nanoparticles, which have an average particle size that is different from the average particle size of the aforementioned core-shell catalyst particles, and which contain the aforementioned metal shell material, being contained in at least one of the aforementioned polymer electrolyte membrane, the aforementioned anode catalyst layer, the aforementioned anode-side gas-diffusion layer, the aforementioned cathode catalyst layer, and the aforementioned cathode-side gas-diffusion layer.