PURPOSE: To permit the series connection of a plurality of kinds of spiral heat- generating bodies by welding through a technique, in which working accuracy and the like are not requested, positioning such as coaxial property and the like are facilitated and simplified in the technique.

CONSTITUTION: A sheath heater is formed of first and second spiral resistors 3, 4, having different positive resistance temperature coefficient and connected in series, and a sheath 2, in which the spiral resistor bodies 3, 14 are buried in heat resistant insulating powder. The connecting ends 20, 21 of the first and second spiral resistor bodies 3, 14 are formed so as to have the same outer diameter substantially and form a closely contacted wound part having smaller coil pitch than the other coil parts. The connecting ends are abutted against each other and are connected through welding such as laser welding or the like whereby the first and second spiral resistor bodies 3, 4 are connected in series.