When a pemanent magnet is taken in and out through the center of a coil shaped conductor, the magnetic field changes and a current flows through the conductor. this is called electro-magnetic induction operation. High frequency induction heater makes induction current(eddt current) flow across the heated material by flowing an AC current through a coil instead of a permanent magnet using this electro-magnetic induction operatiom, and generating alternating magnetic flux. This induction current generates Joule heat by eddy current loss, and the heating using the heat generated this way is called induction heating. In this case the characteristics of the eddy current is that the eddy current tends to be induced densely upon the material area near the coil, and coarsely flow into the mateial. Because energy is concentrated onto the necessary area of the heated material, enabling efficient and rapid heating, the equipment can raise productivity and operability.     δ=5.03√ρ : μF [㎝] (F=주파수(Hz), μ=투자율(steel=1), ρ=μΩ㎝) 소입 깊이에 따른 가열시간과 출력 효율의 관계A