PURPOSE: To install the detection part of a detecting apparatus easily and at a low cost by installing said detection part of the detecting apparatus for detecting the distribution of thread thickness and thread-breakage onto the exit of the thread passage of an air nozzle body into which a thread which advances with a prescribed tension is inserted and air stream is allowed to act onto the thread.

CONSTITUTION: A long rectangular insertion hole 10 is formed in concaved form onto the outlet if a thread passage 2 on an air nozzle body 1, and a luminous body 11 and a light receiving body 12 which constitute the detection part of a thread-breakage detecting apparatus are installed in opposed state onto the insertion hole 10. The light irradiated towards the light receiving body 12 from the luminous body 11 is allowed to cross the whole thread passage 22, and the thread-breakage is detected in a control circuit 14 from the variation of the light received in the case when the thread Y is cut. When there is a distribution in the thickness of the thread Y, and the amount of light in a certain time exceeds a prescribed amount or is less than a prescribed amount, the thread Y is detected as abnormal one in the control circuit 14.