The heat treatment apparatus includes: a processing chamber which accommodates a processing object; a heating unit which heats the processing object accommodated in the processing chamber; a temperature detecting unit which detects an internal temperature of the processing chamber; and a controller which sets a second setting temperature identical to as a temperature detected by the temperature detecting unit when the temperature detected by the temperature detecting unit falls below a predetermined first setting temperature due to an external disturbance; controls the heating unit so that a third setting temperature between the second setting temperature and the first setting temperature becomes identical to the temperature detected by the temperature detecting unit; and controls the heating unit so that the first setting temperature becomes identical to the temperature detected by the temperature detecting unit after the third setting temperature becomes identical to the temperature detected by the temperature detecting unit.