PURPOSE: To execute quenching while reducing the development of oxidized scale by dipping a steel material being held both the end parts with electrodes into water, conducting the electric current from both the electrodes to heat the steel material, holding at a prescribed temp. with pulse oscillation of conductive current and successively cooling with water.

CONSTITUTION: In the condition of clamping both ends of a pipe-like steel material 1 by the electrodes 3, 3 the steel material is dipped into a vessel 4 incorporating hydrogen as liquid for cooling 2, and by conducting the current from both the electrodes 3, 3, the steel material is heated to the necessary quenching temp. by the resistant heat of the steel material 1. After raising the temp., the pulse oscillation of the conductive current is executed to keep the temp. of the steel material 1, and after the pulse treatment is continued for a time during which the carbide in the steel material sufficiently comes to solid solution, the conduction of current is stopped. Thereafter, immediately, water 2 is stirred to rapidly cool and quench the steel material 1. As the content of oxygen in the water is extremely low, the oxidized scale developed on the steel material surface is slight, compared with the quenching in the air, and the quenching is uniformly executed in good thermal efficiency.