A heat treatment apparatus includes a chamber for receiving a substrate therein, and a measurement part for measuring an air particle concentration in a processing space provided in the chamber. An air particle concentration in the processing space provided in the chamber is measured by the measurement part. The air particle concentration is correlated with the number of particles attached to a substrate received in the chamber. Accordingly, by conducting a particle test after the air particle concentration in the processing space is lowered to an air particle concentration corresponding to the number of particles existing on the substrate which can pass the particle test, the number of times the particle test should be conducted after maintenance of the heat treatment apparatus can be reduced.
