The invention provides a temperature-measuring device and a temperature-measuring method. The surface density of projections formed on a thin metal film of a temperature-measuring member having the metal film having been subjected to a temperature profile is calculated with a number-calculating section according to image data fed into an arithmetic processing unit through an optical microscope, CCD camera, and I/O board. The maximum temperature of the object is determined with the temperature-calculating unit according to the surface density and data on the maximum temperature and surface density previously stored in memory. Furthermore, a temperature-measuring member constituted by a thin aluminum film arranged on a substrate is used. A reduction in the reflectivity of the film due to projections formed on the film surface according to a temperature profile to which the member has been subjected is measured. The maximum temperature in the temperature profile is estimated according tothe reduction in reflectivity.