A fixing device that fixes a toner image to a medium, includes: a heating body rotatably supported; an auxiliary heating member disposed along an inner surface of the heating rotation body; a temperature sensor facing the inner surface via the auxiliary heating member; a first elastic body configured to press, via a first force, the temperature sensor against the inner surface; and a second elastic body configured to press, via a second force, a sliding member against the inner surface. A product of a distance from a center of the auxiliary heating member to the first elastic body and the first elastic force is equal to a product of a distance from the center to the second elastic body and the second elastic force.