A composite membrane material characterized by comprising a hydrogen-permeable membrane which is selectively permeable to hydrogen and is formed by rolling to a thickness of 30 μm or less which is difficult for the membrane by itself to retain its shape, and a shape-retention mesh which is disposed on at least one side of the hydrogen-permeable membrane and is composed of a wire of a high-melting metal which does not cause thermal diffusion into the hydrogen-permeable membrane, wherein the hydrogen-permeable membrane and the shape-retention mesh are superposed and subjected to a pleat processing in a non-bonded state so that they are separable and the hydrogen-permeable membrane has a surface area increased at least 3 times per unit area. This material is used to constitute a hydrogen separation element.