A fixing device includes a pressing roller, a fixing belt disposed to be rotated by the pressing roller around a rotation axis of the fixing belt, a pressing member disposed within the fixing belt and to press a portion of the fixing belt toward the pressing roller, a pair of rotation ring members to support corresponding ends of the fixing belt respectively and being rotated by the fixing belt, and a pair of flange members to rotatably support the pair of the rotation ring members respectively, in which a rotation ring member of the pair of rotation ring members is an inclined state towards the fixing belt on a corresponding flange member, in which, with respect to the rotational axis of the fixing belt, an area of the rotation ring member opposite to a contacting area of the rotation member contacting with the pressed portion of the fixing belt protrudes more toward the fixing belt than the contacting area.