A fixing device includes an endless belt, a nip member, a heater, a reflecting member, a load receiving member, and a protective member. The endless belt has end portions in the first direction and a middle portion defined between the end portions. The nip member is configured to contact an inner circumferential surface of the endless belt. The heater is disposed inside the endless belt. The reflecting member is entirely disposed on a nip-member side with respect to the heater and is configured to reflect radiant heat emitted from the heater toward the inner circumferential surface. The protective member is disposed between the middle portion of the endless belt and the heater and on a side opposite to the nip member with respect to the heater, and is configured to allow light to pass therethrough. The protective member is fastened to the load receiving member.