To eliminate troubles, e.g. recrystallization of a sublimate onto a substrate, by dividing the oven in an apparatus being used in a process for firing the substrate formed with a resist pattern into two, exhausting the air powerfully in the preceding chamber and performing firing in the following chamber while circulating the air.

At the time of firing a substrate formed with a resist pattern containing a sublimable component, an oven is divided into two. The air is not circulated in the oven of a preceding chamber for carrying in the substrate 3 formed with a resist pattern through a carry-in port but an air inlet 4 is provided and the substrate is heated while removing sublimates quickly by forced exhaustion through an air outlet 5 at a rate of exchanging the air three times as much as the volume of the oven in about one min, for example. Subsequently, the substrate 3 is carried into a following chamber 2 where it is passed through a passage arranged with a duct collecting filter and a heater 7 for sustaining the environment and temperature while circulating the air before finishing firing.