To provide an induction heating device with less failure, by providing a new method for detecting contacts between an induction heating coil and a work.

A hardening device 1 is provided with a high-frequency power supply 2 with a heating unit 3 connected. The heating unit 3 includes a current transformer 11, and an induction heating coil 10 is connected to its secondary side through a secondary side electric system 33. The induction heating coil 10 includes a heating processing part 31 for heating a processed object, and two conducting parts 32. At the conducting parts 32, core parts 35 are connected, respectively, and induction current flowing in a coil 38 for current detection mounted on them, can be detected. Signals of the coil 38 for current detection are inputted into a control device 5, always monitored, and compared. When a difference of those exceeds a preset value, an alarm signal is emitted from the control device 5.

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