A fixing device includes: an induction coil; heating rotator; pressurizing rotator disposed to face the heating rotator; fixing nip; and magnetic core unit. The heating rotator is disposed in a region through which a magnetic flux generated by the induction coil passes and rotates about a first rotational shaft. The magnetic core unit forms a magnetic path circularly encloses the induction coil. The magnetic core unit includes arch core portions and a core supporting member supporting these portions. The arch core portions each have an arch shape facing the heating rotator across the induction coil and are arranged at intervals in a direction of the first rotational shaft. Each arch core portion has first engaging portions formed respectively at both ends thereof and a core main body formed between the first engaging portions. The core supporting member has second engaging portions with which the first engaging portions are engageable.