PURPOSE: To make it possible to weld a laminated part by means of high-frequency heating by pressing instantaneously Teflon laminated sheets during high-frequency heating and fusing and by destroying the surface of the fluoro resin.

CONSTITUTION: The Teflon laminated sheets to be welded are put one upon another and a groove part of an upper electrode 1 of high-frequency heating is thereon put to contact the material to be welded. This upper electrode 1 is a comb-shaped flat plate and have groove cuttings whose depth is larger than the thickness of two laminated materials to be welded. The electric source is turned on to the high-frequency device set in this way and high-frequency heating is carried out with an ordinary pressure of the device as the first pressure to melt a part of a thermoplastic sheet except the laminated fluoro resin. During the melting, a pressure which is more than three times of the ordinary pressure is instantaneously applied as the second pressure and the surface of the laminated fluoro resin is thereby destroyed and the molten part of the thermoplastic sheet flows into the destroyed parts and welded. By such a method, the economy becomes better and the quality of the product is stabilized because of no need to peel off the fluoro resin.