NOVELTY - A catalyst is obtained by supporting catalytically active component in a carbon carrier. The catalytically active component comprises metal containing platinum (10-80 %mass) with respect to total amount of carbon carrier. The ratio of particle diameter (Dxrd) of platinum computed by formula of Scherrer using the half value width of the (111) peak, and particle diameter (Dec) of platinum estimated from hydrogen desorption wave obtained by electrochemical measurement of the catalyst, is 0.6-1.4.    USE - Catalyst is used for polymer electrolyte fuel cell used as power supply for portable computer and communication apparatus.    ADVANTAGE - The catalyst has excellent catalytic activity and durability, and narrow width of macroscopic size distribution. The polymer electrolyte fuel cell formed using the catalyst is economical and has high energy density. The reduction of catalyst active surface area is prevented by aggregation of catalyst particles, and coating of polymeric protective agent.    DETAILED DESCRIPTION - A catalyst is obtained by supporting catalytically active component in a carbon carrier. The catalytically active component comprises metal containing platinum (10-80 %mass) with respect to total amount of carbon carrier. A background is deleted from diffraction pattern obtained by X-ray-diffraction measurement of the catalyst. Peak-width (b)1/4 in the 1/4 height with respect to height of a peak (111) of the face-centered cubic lattice of the platinum in the diffraction pattern, and peak-width (b)3/4 in 3/4 height with respect to height of the (111) peak are calculated. The (111) peak is assumed to be sum of a Gaussian function and a Lorentz function. Peak-width (b)'1/4 in height of 1/2 with respect to the height of the (111) peak and (b)'3/4 are respectively computed from (b)1/4, and (b)3/4. The ratio of particle diameter (D1/2(h/4)) and particle diameter (D1/2(3h/4)) of platinum computed by formula of Scherrer using (b)' 1/4 and (b)' 3/4, respectively, is 0.9-1.1. The ratio of particle diameter (Dxrd) of platinum computed by formula of Scherrer using the half value width of the (111) peak, and particle diameter (Dec) of platinum estimated from hydrogen desorption wave obtained by the electrochemical measurement of the catalyst, is 0.6-1.4.