Abstract: A high-frequency induction heating apparatus for heating a material includes a voltage source, a high-frequency inverter coupled to the voltage source for feeding an alternating current, and a coil for applying the current to the material to induce eddy currents therein and heat the material. A frequency control device controls the inverter to cyclically feed a first current having a first frequency and a second current having a second frequency higher than the first current to substantially simultaneously heat an inner portion and an outer portion of the material, respectively. The control device also may cyclically switch the voltage level of the output of the inverter between a first voltage level and zero volts to change the power output thereof. The control device apparatus has a switching cycle time that is shorter than the thermal time constant of the material.