To work a large number of nozzles in a short time with excellent accuracy in a working method to be applied to a tube stay which is mounted on an external wall, body part or an end plate knuckle part of a tank, and the welding groove shape of which is of saddle shape.

When a work 5 is set on a female die 3 to which an interlayer liner is fitted to a center recessed part, a male die 2 is loaded on the work, and the male die 2 is wholly surrounded by an upper outer frame 1 and pressed from an upper side, an R-shaped projected part of saddle shape formed in a lower surface of the male die 2 forms a welded groove part of an upper end part of the work 5 into saddle shape. The interlayer liner 4 fitted to the center recessed part of the female die 3 is subjected to the pressure and useful in manufacturing the products of the same dimensions. The upper outer frame 1 prevents collapse of the groove part, deformation of circularity, and uneven wall thickness caused in the working.