Provided are a metal belt which is improved in wear resistance, thermal conductivity, thin wall designs, heat resistance and flexibility, a fixing belt in which this metal belt is used, and a high durability and high reliability heat fixing device which has this fixing belt. This metal belt is made of a nickel-iron alloy manufactured by an electroforming process, and the nickel-iron alloy satisfies relationships expressed by the following equations: 0.001.ltoreq.S.ltoreq.0.13, and (1) 85.times.S+3.ltoreq.F.ltoreq.350.times.S+3 (2) wherein S represents a sulfur content (mass %) and F represents an iron content (mass %).