PURPOSE: To improve reliability of operation by mounting an air injecting nozzle, connected to a flow pipe built in a main unit, directed to a sensor surface so as to hold it always clean, in a balloon control device used in the case of winding back a fine spinning tube thread, produced by a fine spinning machine, by a winder.

CONSTITUTION: Both a tubular balloon breaker 15 formed so as to cover a head part of an extended objective tube thread 1 and a photoelectric tube type sensor 16 of always detecting the uppermost end 20 of a thread layer of the tube thread 1 are secured to a specific position of a bracket 14. The bracket 14 is mounted in a lift lever built in a machine base, to hold the bracket 14 in a position of prescribed height through the lift lever by a detection signal of the sensor 16. In a device thus obtained, an air injecting nozzle 21, connected to a flow pipe built in a main unit, is provided so as to wipe a surface cleaned of the sensor 16 by air injected from this nozzle. An air pipe for Mach splicer used in an thread ending device, air pipe used in a suction mouth, etc., are used in an air source.