Disclosed is a catalyst powder contained in an electrode, wherein the catalyst powder includes a catalytic substance supported on a conductive powder, the catalytic substance being comprised of at least a catalyst, the weight ratio of the catalytic substance to the catalyst powder is in the range of 55 to 75 wt %, and the areal density of the catalytic substance is in the range of 1 to 3 mg/cm.sup.2. Also disclosed is a catalyst electrode including a catalyst powder and a solid polymer electrolyte, the catalyst powder including a catalytic substance supported on a conductive powder, the catalytic substance being comprised of at least a catalyst, wherein the weight ratio of the catalytic substance to the catalyst powder is in the range of 55 to 75 wt %, and the areal density of the catalytic substance in the catalyst powder is in the range of 1 to 3 mg/cm.sup.2. Further disclosed is an electrochemical device including a plurality of electrodes, and an ionic conductor sandwiched between the electrodes, wherein the above-mentioned catalyst electrode constitutes at least one of the plurality of electrodes.