PURPOSE: To provide a versatile bonding method by high frequency induction heating which is easily employed and particularly suitable for bonding a large and a long material to be bonded by applying a solvent which swells the material on its surface and applying high frequency to the surface with a high frequency induction heating apparatus.

CONSTITUTION: A thermoplastic polymer such as chlorinated polyethylene and polyvinyl chloride is bonded by high frequency induction heating. In this method, a solvent including methylethyl ketone and toluene which swells a material 5 to be bonded is applied on its surface 2. High frequency is applied to the surface 2 with a high frequency induction heating apparatus including a high frequency welder based on a flat plate electrode and a high frequency sewing machine based on a roller current 3. The frequency generally used in this method is 40.68 or 27.12MHz of industrial allocation.