TECHNOLOGY FOCUS - POLYMERS - Preferred Process: The process preferably involves: forming a dendritic structural member comprising a catalyst precursor by a vapor phase method; providing a coating layer comprising an electrolyte with proton conductivity on a surface of the dendritic structural member; applying the dendritic structural member having the coating layer to at least one surface of a polymer electrolyte membrane (1) to form a membrane electrode assembly precursor; incorporating the membrane electrode assembly precursor into a fuel cell unit; and energizing the fuel cell unit. The vapor phase method is a sputtering method, and the step of subjecting the dendritic structural member having the coating layer to the reduction treatment involves the step of electrochemically reducing the dendritic structural member with protons and electrons; the step of bringing a gas containing a reducing agent into contact with the dendritic structural member to effect reduction; or a step of bringing a solution containing a reducing agent into contact with the dendritic structural member to effect reduction. The step of electrochemically reducing the dendritic structural member with protons and electrons involves a two-stage reduction process including the first stage of reducing a surface of the catalyst precursor and the second stage of reducing an inside of the catalyst precursor. The energization is performed in two stages by supplying hydrogen to an anode electrode of the fuel cell unit and sweeping a current. The process further involves between the step of forming the dendritic structural member comprising the catalyst precursor by the vapor phase method and the step of providing the coating layer on the surface of the dendritic structural member, the step of providing to the surface of the dendritic structural member an Si compound comprising Si (silicon), -OH (hydroxyl) bonded to the Si or a group which is bonded to the Si and becomes -OH through hydrolysis, and a hydrophobic group; and between the step of providing the coating layer on the surface of the dendritic structural member and the step of subjecting the dendritic structural member having the coating layer to the reduction treatment, the step of providing to the surface of the dendritic structural member a Si compound comprising Si, -OH bonded to the Si or a group which is bonded to the Si and becomes -OH through hydrolysis, and a hydrophobic group. Preferred Components: The dendritic structural member comprising the catalyst precursor is a dendritic structural member containing platinum oxide or a dendritic structural member containing a composite oxide of platinum oxide and an element except platinum. The coating layer comprises an electrolyte having proton conductivity (preferably perfluorosulfonic acid polymer or hydrocarbon-based polymer electrolyte). The thickness of the coating layer is 1-200 nm. The group which becomes -OH through hydrolysis is any one of H, OR (where R is alkyl group having less than or equal to 6 carbon atoms) and Cl. EXAMPLE - No suitable example given.