According to the basic principle of electromagnetic induction, the three-phase power frequency alternating current is rectified and converted into direct current, which is then converted into adjustable intermediate frequency current to supply a load composed of a capacitor and an induction coil (the coil and capacitor can be connected in parallel or in series). High density magnetic lines of force are generated in the induction coil, and the metal material contained in the induction coil is cut, generating large eddy currents in the metal material. This type of eddy current also has some properties of intermediate frequency current, that is, the free electrons of the metal itself flow in a resistive metal body to generate heat. For example, if a metal cylinder is placed in an induction coil with alternating intermediate frequency current, and the metal cylinder is not in direct contact with the induction coil, the temperature of the energized coil itself is already very low. However, the surface of the cylinder is heated to redness or even melting, and the rate of redness and melting can be achieved by adjusting the frequency and current strength. If the cylinder is placed in the center of the coil, the temperature around the cylinder is the same, and the heating and melting of the cylinder do not produce harmful gas or strong light to pollute the environment.