PURPOSE: To measure temperature on the surface of a molten liquid inside a crystal pulling furnace with high accuracy, continuously and with the good following property of a change in the temperature by removing a beam of scattered light by using a radiation thermometer.

CONSTITUTION: A molten liquid 2 inside a crucible 1 is heated by a heater 3, and a single crystal 1 is grown. A beam of thermal radiation light from a measuring point A on the molten liquid 2 and a beam of radiation light (scattered light) which is reflected at the measuring point A and which comes from a radiation source (a measuring point B) are incident on a radiation thermometer 6. A beam of thermal radiation light from the measuring point B is directly incident also on a two-color radiation thermometer 7. Output signals from the radiation thermometer 6 and the two-color radiation thermometer 7 are input to an operation part 8, and a temperature at the measuring point A on the molten liquid 2 is computed and output. An output signal from the operation part 8 is input to an electric-power supply and control part 9. The electric-power supply and control part 9 controls the electric power of the heater 3 according to an input signal, and it maintains the temperature of the molten liquid 2.