To provide a heat treatment apparatus which cools a material to be treated in a short time.

A steam supply pipe 2 for heating and a cooling medium supply pipe 3 for supplying a cooling medium having a prescribed pressure are connected to the upper part of a tightly closed valcanizer 1. An outside communicating pipe 4 for communicating the inside of the vacanizer 1 with the outside is connected to the lower part of the valcanizer 1. In the case of being cooled, the material to be treated in the valcanizer 1 is cooled in a short time by discharging steam from the outside communicating pipe gradually while supplying a prescribed quantity of the cooling medium from the cooling medium supply pipe 3.