PURPOSE: To halve the energy consumption, and to contrive the shortening of the number of days for manufacturing the heat treated product, by arranging the heat treating equipment on the extension of the rolling line so as to be directly connected to the steel material finishing mill, and by passing the steel material through said heat treating equipment under the condition that the steel material is subjected to a tensile stress.

CONSTITUTION: The heat treating equipment including the heating apparatus 2, the hardening apparatus 3, the tempering apparatus 4, etc., is arranged in series on the extension of the rolling line to which the rolled material P is being restrained, so as to just follow to the run-out side of the steel pipe, steel bar, etc., finishing mill 1; the rolled material P is passed through this heat treating equipment while the rolled material P is being subjected to a tensile stress. Hereupon, the high pressure water is jetted from circumferentially arranged notches 6 of the cylindrical wall of the hardening apparatus 3 in the direction to advance the hardened material (rolled material P) toward the run-out side of the hardening apparatus 3; hererby, the material P is carried in the floating condition on the pass line. According to this heat treating method, the energy consumption can be halved as compared with the conventional method, and besides, the cheap equipment investment makes the heat treating capacity of existing equipment possible to be several times increased.