PURPOSE: To prevent generation of carburization on the surface of a quenching material, and to elevate brightness of the surface, by vacuum-heating the quenching material to a prescribed temperature, and after that, cooling it in a liquid by a specific degree of vacuum, when executing bright quenching of the quenching material.

CONSTITUTION: A quenching material is heated to a prescribed temperature by a high degree of vacuum corresponding to its kind. Subsequently, it is cooled in a liquid in a reduced pressure state which is not recovered and is ≤400Torrs in a degree of vacuum, a boiling phenomenon is generated against a vapor film generated by gasification and thermal cracking of the quenching liquid on the surface of the quenching material, and disappearance of the vapor film is quickened by vigorous self-agitation. As for the quenching material, carbon tool steel, alloy tool steel, etc. as well as general carbon steel are available, and as for the quenching liquid, it is desirable to use mineral oil. Also, as necessary, the quenching liquid can be agitated and jetted suitably.