To provide a method that dispenses with the structure of a large scale device for the purpose of forming ultra-high vacuum atmosphere, that eliminates difficulty of alignment between the surfaces to be joined under such atmosphere, and that performs welding simply and precisely between solid bodies.

The welding of two or more members is constituted of such indispensable processes that a monomolecular built-up film containing a metallic ion is formed at least one of the member surfaces to be joined (A), that the members are closed adhered with each other through the surfaces to be joined (B) and that an electric field is applied to the surfaces to be joined (C); and, if desired, supplementary processes of heating (D) or irradiating with a laser beam (E) are added.