PURPOSE: To prevent the adsorption of a heat-resistant, pressure-resistant buffer board to a press heating plate by placing the heat-resistant, pressure-resistant buffer board with a grooved surface between the press heating plate and a pair of forming, jigs having a multilayer copper-clad board between said forming jigs.

CONSTITUTION: On a carrier plate 1, a plurality of inner layer printing and wiring boards, surface printing and wiring copper foils and a resin-impregnated material for bonding these are placed in a multilayer copper-clad board 6; it is then placed between a forming mirror board 5 and a forming jig board 4; and heat-resistant, pressure-resistant buffer board or a buffer paper 2 is arranged at the tom and bottom of said assembly. Moreover, a surface grooved buffer board 3 having surface grooves 3a at the top is installed and then subjected to heating and pressuring forming process. When a press heating plate 7 is opened after the heating and pressuring forming process, air inflow becomes easier to the space between the surface grooved buffer board 3 and the press heating plate 7 by means of the surface grooved buffer board 3, thereby preventing adsorption.