An object of the present invention is to provide an induction heater and an induction heating method capable of heating by induction a work in which a gear portion and a shaft are integrated.An induction heater for a gear portion and a stepped shaft is arranged in such a manner that a first heating coil (annular coil) surrounds the gear portion and that a second heating coil (linear coil) faces the stepped shaft in an axial direction. Alternating currents of different frequencies are supplied to the first heating coil 1 and the second heating coil. Further, a part of the second heating coil is arranged so as to come opposite a boundary between the gear portion and the stepped shaft, thereby connecting a hardened pattern of the gear portion by the first heating coil and a hardened pattern of the stepped shaft by the second heating coil.