A fixing device includes a tubular flexible metallic fusing member, a heater, a nip member, and a backup member. The fusing member has an inner peripheral surface defining an internal space. The heater is disposed in the internal space. The nip member is disposed in the internal space for receiving radiant heat from the heater and has a contact surface in sliding contact with the inner peripheral surface. At least the contact surface is provided with a protection layer having a hardness higher than that of the inner peripheral surface. The backup member nips the fusing member in cooperation with the nip member.