A heat-bonding apparatus and method of manufacturing a heat-bonded product without overheating during cooling thereof after the completion of the heat-bonding, where the object can be cooled in a shorter time than the conventional when the heat-bonding is performed in a vacuum. A heat-bonding apparatus having a vacuum chamber for housing an object to be heat-bonded and a buffer part, a heater for applying heat to the buffer part placed into contact with the object, an object temperature sensor for detecting a temperature of the object heated through the buffer part, a buffer temperature sensor for detecting a temperature of the buffer part, a vacuum breaker for breaking the vacuum, and a controller for operating the vacuum breaker to break the vacuum when a temperature difference between a temperature detected by the object temperature sensor and a temperature detected by the buffer temperature sensor falls within a range of specified temperature difference.