A fixing device includes a fixing member including a heat generator and an induction heater to heat the fixing member by electromagnetic induction. The induction heater includes an excitation coil, a ferromagnetic core to form a magnetic path to direct magnetic flux arising from the excitation coil to the fixing member, and a holder to hold the excitation coil and the ferromagnetic core. The holder has a surface facing the heat generator. The surface has a plurality of slits extending parallel to a direction of rotation of the fixing member. The ferromagnetic core is coupled to the holder and covers an open bottom portion of each slit of the plurality of slits to form a plurality of bottomed grooves.