PURPOSE: To maintain the tight contact between metallic honeycomb core materials and upper and lower metallic plates and to execute secure brazing by forming the upper and lower metallic plates to a hermetically sealed box- shaped body, inserting the metallic honeycomb core materials therein, reducing the pressure in this box-shaped body and subjecting the box-shaped body to heating for the purpose of brazing.

CONSTITUTION: The four sides of the upper and lower plates 1, 1' of the honeycomb panel are bent and the end faces of the raised parts 3, 3' of these upper and lower plates are butted against each other. The honeycomb core materials 4 made of an aluminum alloy consisting of many hexagonal cells are inserted therein and the butt parts of the raised parts 3, 3' of the upper and lower plates 1, 1' are welded to form the box-shaped body. A pipe 5 is mounted in a part of the upper and lower plates of the hermetically sealed box-shaped body and is connected to a vacuum pump. The pressure in the box-shaped body is then reduced and thereafter, the pressure is restored by pure oxygen and the pipe 5 is closed. This box-shaped body is put into a furnace and is heated, following which the box-shaped body is taken out of the furnace and the pipe 5 is cut. The honeycomb panel is thus obtd.