To reduce not only expenses for preparing a Y shaped tube but also troublesome welding processes by arranging a pipe bulging hole for bulging a manifold part composed of circuit patterns of the upper and the lower surfaces at one place and introducing compressed air from the one place of the pipe bulging hole to bulge the pipe.

In a manufacturing method for three layered roll boned panel in which an intermediate plate and plates superposed on the upper and the lower surfaces thereof respectively are rolled, and bulging the circuit parts among the intermediate plate and the upper plate and the lower plate; the pipe bulging hole 5 is arranged on one side surface of one of the printed circuits among the intermediate plate and the upper plate and the lower plate. An opening hole part 9 is holed on the intermediate plate so as to communicate the upper and the lower circuit parts between the pipe bulging hole and the manifold part 6, and an upper and a lower printed circuit patterns are branched in the right and the left directions nearer the manifold part than this opening part and the compressed air is introduced from one pipe bulging hole. By this method, the compressed air is supplied to the manifold parts on both the upper and the lower surfaces altogether to simultaneously bulge the upper and the lower circuit parts.