A catalyst includes a conductive carrier and catalyst particles. The catalyst particles are supported on the conductive carrier and have a composition represented by formula 1, below. An area of a peak derived from a metal bond of a T-element is 15% or more of an area of a peak derived from an oxygen bond of the T-element in a spectrum obtained by X-ray photoelectron spectroscopic method. Pt.sub.xRu.sub.yT.sub.z (1) where the T-element is at least one element selected from the group consisting of V, Nb and Hf, x is 30 to 60 at. %, y is 20 to 50 at. % and z is 5 to 50 at. %.