A fixing device includes a fixing belt, a heating source and a fixing roller. The fixing belt has a sheet passing part and a non-sheet passing part. The fixing roller includes an elastic layer including first and second elastic parts. The first elastic part is provided on an inner diameter side of the sheet passing part. The second elastic part is provided on an inner diameter side of the non-sheet passing part. A gap is formed between a part of the elastic layer and the fixing belt in a state where the fixing belt is not heated. The part of the elastic layer is in close contact with the fixing belt in a state where the fixing belt is heated. The first elastic part includes a small-diameter part having a smaller external diameter than a part with a maximum external diameter of the second elastic part.