To provide a thermal stability measuring device in a drying process, allowing the thermal stability of a combustible substance in a dryer etc. to be appropriately evaluated.

The thermal stability measuring device in a drying process measures the heat generation behavior of a drying object article M made of powder or a granular substance in the drying process of drying the drying object article M, and includes a heating source 12 heating a part of the surface of the drying object article M while a part of the surface is isolated from ambient gas, and a temperature sensor 34 for measuring a temperature in the drying object article M in a state in which the drying object article is heated by the heating source 12. The heating source 12 can hold the drying object article M in such a manner that a part to be contacted with the ambient gas is formed on the surface of the drying object article M. A heat generation phenomenon caused by the oxidation reaction of the drying object article generated when the drying object article is dried in a state near the actual drying process is reproduced, and a heat generation behavior caused by the oxidation reaction of the drying object article M in the drying process is obtained.