A fixing device according to an embodiment includes a fixing belt, a pressurizing roller, a supporting member and a heating member. The fixing belt is supported to be capable of circularly moving and is formed endless. The pressurizing roller comes into contact with an outer circumferential surface of the fixing belt and forms a nip for holding a sheet. The supporting member is disposed on an inner side of the fixing belt and extends in an axial direction of the fixing belt. The heating member is disposed on the inner side of the fixing belt and supported by the supporting member and extends in the axial direction of the fixing belt. If the pressurizing roller does not pressurize the fixing belt, end portions of a second principal plane opposite to a first principal plane on the pressurizing roller side of the heating member are separated from the supporting member.