Abstract: A temperature-measuring instrument especially for measuring high temperatures in pressure reactors. It comprises a sheathed thermocouple which is mounted in an inner ceramic element which is closed at one end. This inner element is inserted into a molybdenum element which is also closed at the same end and is surrounded in turn by an outer ceramic element. The annular space between the molybdenum element and the ceramic element is filled with a pressed ceramic mass. A flanged joint joins the molybdenum element to a ball joint which is in turn joined via bellows to a pressure-resistant bushing.