PURPOSE: To easily detect the temp. of an object to be measured, by detecting the temp. of the object to be measured by receiving the same at a desired remote area.

CONSTITUTION: When a throw-in thermometer is thrown in a molten metal being a measuring article, a wt. 2 is acted and the thermocouple 1 provided to the leading end part of said thermometer is connected with the molten metals as sunk in said molten metal and, if said thermocouple 1 is sunk up to a definite position, it is not further sunk because of the specific gravity of the metal and becomes stable as is floated at the definite position. The detection signal based on the measurement of temp. by the thermocouple 1 arriving the object to be measured as mentioned above is sent to the transmitter 3 connected to a battery 4 and amplified to an analogue signal having a sufficient gain while the analogue signal is converted to a digital signal to be transmitted by radio. By receiving this transmission at a desired remote area, measured temp. is detected.