A fixing device forms, with use of an endless belt and a fixing roller that are positioned facing each other, a fixing nip by placing the endless belt in contact with the fixing roller while causing a pressing member to press the endless belt from an inner side thereof against the fixing roller, and fixes an unfixed image onto a recording medium when the recording medium passes through the fixing nip. The fixing device includes (i) a sheet member that is provided between the endless belt and the pressing member and thus reduces friction therebetween, (ii) a supporting mechanism that movably supports the sheet member, and (iii) a sheet member moving part that, when a predetermined condition is not satisfied, keeps the sheet member at rest, and when the predetermined condition is satisfied, moves the sheet member in a certain direction by a predetermined amount.