The present invention provides a concentration distribution for a platinum group metal component in a catalyst with which catalyst activity can be increased, and to provide a method for supporting a platinum group metal with which this concentration distribution can be achieved. The present invention is a solid acid catalyst that is made up of porous catalyst pellets exhibiting solid acid characteristics, and a platinum group metal component supported by these catalyst pellets, and that is used in an acid-catalyzed reaction, in which a quotient of dividing the standard deviation of the concentration in a platinum group metal component concentration distribution in the catalyst by an average concentration is 0.4 or less. The method for preparing this catalyst involves a step of preparing a support solution containing a platinum group metal as a cation, and a step of impregnating crystalline, porous catalyst pellets exhibiting solid acid characteristics with this support solution. The present invention also provides a method for isomerizing a hydrocarbon, wherein a solid acid catalyst is brought into contact with a hydrocarbon including at least 70 wt % of a saturated hydrocarbon component having 4 to 10 carbon atoms.