PURPOSE: To simultaneously achieve the main grinding and the finish grinding by operating the work by a device integrated with a wide jet nozzle and a fine jet nozzle in removing a part of a coating covering a plate surface to be resistant in diffusion welding.

CONSTITUTION: An upper surface of a plate 1 consisting of a super-composition titanium alloy is covered with a yttrium oxide coating 2, and when a part 3 of the plate 1 is exposed by removing a part of the coating 2 in such a plate 1, the coating is removed from a widest part of a strip of the part 3 using a wide jet nozzle 4. When the coating is removed in a contour of the strip of the part 3, fine jet nozzles 5, 6 which are installed in an inclined manner are used. The fine jet nozzles 5, 6 are allowed to be sufficiently separated from or directly follow the wide jet nozzle 4 during the cutting, and an edge part is clearly formed thereby.