PURPOSE: To attain to conserve heat energy, by providing a preheating part, a heating part and a soaking part while heating the heating part by inexpensive fuel such as kerosene and/or gas and utilizing the exhaust gas from said heating part.

CONSTITUTION: A steel wire heating furnace 1 for an oil tempered wire consists of a soaking part 4 heated by an electric heater 9, a heating part 3 and a preheating part 2 utilizing the gas exhausted from two parts. This furnace 1 allows a steel wire 8 to pass through a steel wire protective pipe 7 for preventing oxidation to heat the same and, directly after heating, oil hardening is applied to the steel wire 8. The aforementioned heating part 3 is heated by a combustion apparatus 5 using kerosene and/or gas and partitioned from the soaking part 4 by a partition tool 10.