To detect a state of yarn with high precision by precisely correcting detection sensitivity of a detector on each of yarn clearers.
The detection sensitivity of a detector 32 to output a detection signal in accordance with a state of yarn is adjusted with detection sensitivity in accordance with a driving signal. It has a microcomputer 35 to which the detection signal of the detector 32 is input and which outputs the driving signal. The microcomputer 35 computes a yarn travelling standard value AVEn from an average value of a detection value S at the time when yarn travels for each of yarn clearers 3 and increases and decreases the driving signal in accordance with a result of comparing the detection value S with the yarn travelling standard value AVEn.
MATSUMOTO SHINICHI
HITOSHINA TOMOYUKI
