A fixing device for image forming apparatus includes: a first nip member in a shape of an endless belt and a second nip member that rotates while pressed against the first nip member. A heat source heats at least one of the nip members. A pressure receiver receives pressure applied to the first nip member from the second nip member. A sliding contact has a contact surface that makes sliding contact with an inner surface of an axial end of the first nip member. A supporting mechanism supports the sliding contact to displace the contact surface thereof away from the pressure receiver as the first nip member moves away from the sliding contact along the axial direction. The displacement increases frictional forces between the contact surface and the inner surface of the first nip member, thus suppressing axial displacement of the first nip member from the sliding contact.