A fixing device includes a flexible rotating fixing belt, a pressing member, a heating part, a guide member and a contact force changing part. The pressing member forms a pressing area with the fixing belt. The heating part heats the fixing belt from an outside of the fixing belt. The guide member comes into contact with an inner circumferential face of the fixing belt to support the fixing belt so as to face the heating part. The contact force changing part moves the guide member in directions close to or away from the fixing belt to change a contact force between the guide member and the fixing belt depending on a pressure of the pressing area.