To provide a control device of an induction melting furnace which can detect the phase difference of the output voltage and output current from a power conversion unit with a simple configuration.

A control circuit 10 includes an output voltage signal generation unit 11 which generates an output voltage signal that is an ON signal in a time-domain defined by the rising of an operation signal of an IGBT inverter 42a and the rising of an operation signal of an IGBT inverter 42b, and an output current generation unit 12 which generates an output current signal that is an ON signal between the rising and the next falling of an output current from a power converter 4. Phase difference of the output current and output voltage from the power converter 4 is detected from the output voltage signal and output current signal thus generated.