PURPOSE: To manufacture a jig fit for microwave processing and simplify mechanical processing by constituting the jig of metal beds provided on the opposite side of a pin clamped surface of a material to be heated and gypsum molds fixed to said metal beds and containing water glass of more than given thickness from the bed surface to the side of the material to be heated.

CONSTITUTION: A jig is constituted of metal beds 10 and 11 provided on the opposite side of the clamped surface of a material to be heated and molds 13 and 14 fixed to said metal beds and of given thickness on the side of the material to be heated. Said molds 13 and 14 are constituted of gypsum to which water glass is added and has γ(relative dielectric constant) of 4W6 sufficient to pass microwaves, and are formed into given shapes by mechanical processing. Said molding jig clamps the material to be heated in its intermediate section and presses the same from both sides. Heating is not carried out within 1/4 wave length from a metal plate, while the wave length becomes 1/4 (γ)1/2 in a dielectric material of relative dielectric constant γ. Therefore, in order to heat the whole of the material to be heated encircled with the molding jig, the molds 13 and 14 of said molding jig need at least the thickness of λ/4(γ)1/2 or more from the surfaces of metal beds 10 and 11 and the side of the material to be heated.