A fixing device includes an endless belt, a girder disposed inside of a loop of the endless belt and extending in the width direction, a plate disposed between the girder and the endless belt, a pressing member disposed outside of the loop of the endless belt, a heater disposed inside the loop pf the endless belt, a first support disposed between the plate and the girder, and a second support disposed between the plate and the girder while being away from the first support. The first height of the second support is greater than the second height of the second support. A first difference between the first height of the first support and the second height of the first support is less than a second difference between the first height of the second support and the second height of the second support.