To impart good resistance to caulking and carburization to a welded joined part in the case reaction pipes for manufacturing ethylene or the like by pyrolyzing naphtha as a raw material are joined by butt welding.

The butt welded joint of the metallic composite pipes is composed by laminate-forming of build-up welding layers 14 having resistance to caulking on the inside of the metallic pipe 12 of a base material. The inside of the metallic pipe 12 of the base material which is formed by laminating build-up welded layers is welded by using a filler metal (A) containing 36-49% Cr, 35-63% Ni, 0.5-5% Mo or a filler metal (B) containing 20-49% Cr, 35-80% Ni and one or two kinds of Al and Si of 1.5-5% in the total of (Al+Si) and also the rest part is welded by using a filler metal having component equal to the metallic pipe 12 of the base material.