To provide a material to be welded for butt welding which can reduce contamination of particles into a welded portion after the welding is executed and which can construct piping or a device each enabling realization with high repeatability a ultra-clean atmosphere in which the density of impurity such as moisture or the like is suppressed, and a method of cutting the same. Also to provide a wire used for wire cut electric discharge machine which can prevent reduction of chromium composition in a place adjacent to the welded bead section after the welding is executed. (1) A face to be butted of the material to be welded is cut by a wire cut electric discharge machine. It should be noted that it is preferable that the surface of the wire used for the wire cut electric discharge machine is stainless or chromium and that stainless steel or chromium having a thickness of not less than 0.1 .mu.m is deposited on the cut face. (2) As for the method of cutting, at least a face to be butted is cut by the wire cut electric discharge machine. (3) At least the surface of the wire is made of stainless steel or chromium.