TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preparation (Claimed): Preparation of (I) comprises: e.g. attaching a first catalyst metal particle on a surface of a conductor (5), forming a linear first carbon body on a surface of the first catalyst metal particle, and allowing the first carbon body to support a catalyst; or attaching a first catalyst metal particle on a surface of a first carbon body, forming a linear second carbon body on a surface of the first catalyst metal particle, allowing the second carbon body to support a catalyst, and immersing the first carbon body and the second carbon body in a solid polymer electrolyte solution; or forming a first catalyst metal layer on a surface of a conductor, granulating the first catalyst metal layer by heating treatment, forming a linear first carbon body on a surface of the granulated first catalyst metal layer, and allowing the first carbon body to support a catalyst; or forming a silicon layer on a surface of a conductor, forming a catalyst metal layer on a surface of the silicon layer, granulating the silicon layer and the catalyst metal layer by heating treatment, forming a linear carbon body on a surface of the granulated layers, and allowing the carbon body to support a catalyst; or forming a catalyst metal layer on a surface of a first carbon body or an aggregate of the first carbon bodies, granulating the catalyst metal layer by heating treatment, forming a linear second carbon body on a surface of the granulated catalyst metal layer, allowing the second carbon body to support a catalyst; and immersing the first carbon body and the second carbon body in a solid polymer electrolyte solution. Preferred Components: (I) comprises: (A); a linear first carbon body supporting (A); and a linear or particulate second carbon body, where one end of the first carbon body is electrically connected to the second carbon body. (I) is configured in a layer structure, which comprises (A); a linear first carbon body supporting (A); and a second carbon body, where one end of the first carbon body is electrically connected to the second carbon body, and part of the second carbon body reaches a surface of the layer structure. In (I), a surface of the carbon body is modified with a substituent group capable of supplying a proton by dissociation and where with regard to surfaces of the first carbon body and the second carbon body, at least the surface of the second carbon body is modified with a substituent group capable of supplying a proton by dissociation. The modification with the substituent group includes sulfonization, and the substituent group is a carboxyl group, sulfonyl group, amino group, nitro group and/or a sulfo group. Preferred Process: The preparation of (I) further comprises: modifying a surface of the first carbon body with a substituent group capable of supplying a proton by dissociation; attaching a second catalyst metal particle on a surface of the first carbon body; forming a linear second carbon body on a surface of the second catalyst metal particle; and allowing the second carbon body to support a catalyst; and modifying a surface of the second carbon body with a substituent group capable of supplying a proton by dissociation. EXAMPLE - None given.