PURPOSE: To make a catalyst to be evenly and firmly held by an electrode base, and enhance the activity of the catalyst by preparing a catalyst holding powder consisting of both a carbon powder coated with platinum, and a co-catalyst deposited over the former carbon powder, and applying a mixture of the catalyst holding powder and a binding agent to the electrode base.

CONSTITUTION: A mixture of methanol and water is added with a carbon powder such as acetylene black, polyvinyl alcohol, and chloroplatinic acid. Thus prepared mixture solution is subjected to reflux heating at an appropriate temperature, before the product developed in this solution is filtered off and dried, thus platinum being deposited on the carbon powder. The above carbon powder coated with platinum, next, is dispersed in a solution of a co-catalyst such as tin, titanium, rhenium and ruthenium. After that, the dispersion is put in a container, in which an active electrode and its counter electrode are installed, so as to make the dispersion to flow, and thereby the co-catalyst is electrically deposited over the carbon powder coated with platinum. Thus obtained powder holding the co-catalyst, together with a binder such as polytetrafluoroetylene or polyvinyl chloride, is applied to an electrode base.