the position of the seed crystal 26 is detected by a reference position detector 30 disposed at a height h from the melt surface 16a which outputs a signal indicating the position of the seed crystal 26 to the controller 52 the reference position sensor 30 comprises for example a light source and a photo detector such that the photo detector detects light from the light source interrupted by the tip of the seed crystal 26 and notifies the controller 52 of the interruption of the light so that the controller 52 senses that the tip of the seed crystal 26 has reached the position at the height h from the melt surface 16a also an industrial television camera 28 is disposed at a height l from the melt surface 16a for controlling the diameter of a single crystal the bearing 44 is electrically connected to an output terminal of a direct current dc power supply 46 through a resistor 48 the dc power supply 46 has the other output terminal electrically connected to a base 42 for supporting the rotating shaft of the drum 34 also a comparator 50 is electrically connected to the resistor 48 and the dc power.