A fixing device includes an induction heater disposed opposite a heating rotary body and including a first side core disposed at one end of the induction heater, a second side core disposed at another end of the induction heater in a direction of rotation of the heating rotary body, and a plurality of arch cores arranged in an axial direction of the heating rotary body. Each arch core includes a first vault edge face disposed at one end of the arch core in the direction of rotation of the heating rotary body and contacting a planar face of the first side core and a second vault edge face disposed at another end of the arch core in the direction of rotation of the heating rotary body and contacting a planar face of the second side core.