To send warning signals and stop a frame by quantitatively measure an amount of oiling agent impregnated into yarn and detecting abnormality of the oil impregnated amount deviated from a specified value and also yarn end breakage.

This apparatus is equipped with an oscillation part 5 composed of an oscillation electrode 6 arranged in correspondence to a traveling passage of a yarn 1 in which oiling agent is impregnated and alternating current oscillator 7 for applying alternating voltage to the oscillation electrode 6 and a detecting part 8 composed of a pair of received electrodes 9a and 9b, a differential amplifier 10, a waveform shaper 14, a voltmeter 15, a compactor 16 and relay circuit 17, and abnormality of the oil impregnated amount and yarn end breakage are detected by the detection part 8 and the relay circuit 17 is operated by output of the compactor 16 to inform abnormality of the amount of oil agent impregnated into yarn 1 and yarn end breakage.