A cord-shaped heater 1, having: a conductive wires 5a; an inner-layer covering 7 formed on the outer periphery of the conductive wires 5a; and an outer-layer covering 9 formed on the outer periphery of the inner-layer covering 7, wherein the melting temperature of the inner-layer covering 7 is higher than the melting temperature of the outer-layer covering 9, the inner-layer covering 7 and the outer-layer covering 9 are made of same type of polymer material, and the inner-layer covering 7 and the outer-layer covering 9 are adhered to each other. The cord-shaped heater 1, wherein the conductive wire 5a includes a plurality of conductive wires, and the conductive wires 5a is covered with an insulating film 5b. A sheet-shaped heater, wherein the cord-shaped heater is arranged on a substrate, the substrate has a gap, at least a part of the outer-layer covering is penetrated into the gap of the substrate, and the inner-layer covering is not penetrated into the gap of the substrate.