Fixing device and image forming apparatus incorporating same

A fixing device comprising:

• a rotatable fixing member, comprising one of a roller and a belt;
• a pressing member to press against the fixing member;
• and
• an induction heater serving as a heating source to heat the fixing member, the induction heater including:
• an excitation coil to inductively heat a heat generation layer;
• ferromagnetic cores to form a continuous magnetic path to direct magnetic flux arising from the excitation coil to a predetermined position;
• and
• a holder to hold the excitation coil and the ferromagnetic cores,
• the ferromagnetic cores including multiple arch cores disposed facing an outer surface of the heat generation layer with the excitation coil interposed therebetween and multiple side cores disposed outside the excitation coil in a longitudinal direction of the induction heater so as to face both ends of each of the multiple arch cores,
• the multiple side cores integrally inserted in the holder,
• the holder including a spacer,
• the spacer containing a resin material used in the holder and provided in a close-facing portion located between at least one of the multiple arch cores and at least one of the multiple side cores to form a gap.