The present invention is a catalyst for use in a fuel electrode of a polymer solid electrotype fuel cell which is formed by making a carbon powder support platinum and ruthenium thereon, and is characterized in that the loading ratio between platinum and ruthenium is from 1:2.5 to 1:4 (in molar ratio). It is preferable that the loading density of the catalyst is 40 to 70%. Additionally, it is preferable that a carbon powder having a specific surface area of 600 to 1,200 m²/g is used as the carrier supporting the catalyst particles.