An electric power processing device is provided with an induction heating device (9) that is comprised of an induction heater driving inverter (16) with which an electric power source rectifying capacitor (2) connected in parallel with inverter (3) to drive a motor (4) is connected in parallel, and a resonance circuit (17) provided with an induction heater (18) that is connected with the inverter(16); a comparator (12) that detects a voltage of the electric power source rectifying capacitor (2) and compares the voltage with a reference voltage (11); a switching waveform determining circuit (13) that determines a switching waveform in response to an output of the comparator (12); and a switching element drive circuit (14) that drives a switching element of the inverter (16) in response toan output of the switching waveform determining circuit (13).