A fixing device includes a heating body, a pressuring body, a lateral plate supporting the heating or pressuring body, a first supporting body supporting the heating or pressuring body, a second supporting body including a roller, a tensile spring between the first and second supporting bodies, an eccentric cam, a rotating shaft, a protrusion, a driving part, and a pressing member. The cam is supported between the first and second supporting bodies swingable in the lateral plate and has a depression gradually inclined from an upstream side to a downstream side in a rotation direction. The protrusion is protruded from the rotating shaft and meets the depression. The pressing member presses the cam opposite the protrusion. The cam rotates and meets the roller to shift the second supporting body and to extend and contract the spring, and changes a nip pressure from a first pressure to a lower second pressure.