Fixing device and image forming apparatus incorporating same

A fixing device includes a rotatable fixing member, a pressing member, and an induction heater. The induction heater includes an excitation coil, ferromagnetic cores, and a holder. The ferromagnetic cores include multiple arch cores and multiple side cores. The multiple arch cores are disposed facing an outer surface of a heat generation layer with the excitation coil interposed therebetween. The multiple side cores are 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 are integrally inserted in the holder. The holder includes a spacer. The spacer contains 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.