A fixing device includes a cylindrical fixing member, a pressing member, a bearing and a heat insulating member. The fixing member is heated by a heat source. The pressing member forms a fixing nip between the pressing member and the fixing member. The bearing supports an end portion of the fixing member in a rotatable manner. The heat insulating member is interposed between the bearing and the end portion of the fixing member. The heat insulating member has a cylindrical part and a flange part. The cylindrical part has a slitting groove extending along an axis direction of the cylindrical part. The flange part extends outward in a radial direction of the cylindrical part from one end of the cylindrical part in the axis direction. At least one notch is formed along an outer circumferential edge of the flange part.