PURPOSE: A joint device for a thermocouple unit measuring the temperature of molten steel in a tundish is provided to easily attach or remove a thermocouple unit to a tundish. CONSTITUTION: A joint device for a thermocouple unit measuring the temperature of molten steel in a tundish comprises a fixing frame(310), a closing frame(320), and a tightening block(330). The fixing frame has a locking groove(311) and two or more key grooves(312) and is fixed to the outer shell of a tundish(3). The closing frame has a locking projection(321) which is inserted in the key grooves and advanced into the locking groove by being rotated, and a female thread part(323) on the inner periphery. The tightening block has a male thread part(331) on the outer periphery which is coupled to the female thread part of the closing frame in order to press the closing frame to the fixing frame.
