PURPOSE: To make it possible to sense the yarn breakage in the respective spindles of a spinning frame at a low cost without requiring the patrolling of a yarn breakage sensing apparatus between the respective spindles, by means of a light projecting optical fiber having one end opposite to a running yarn in each spindle of the spinning frame and the other end led to the end of the machine frame.

CONSTITUTION: One end 9 of each optical fiber 8 is placed opposite to a yarn 6 between a drafting apparatus 2 and a snail wire 3 of a spining frame, and each optical fiber 8 is fixed on a machine frame 10. The other end thereof 11 is led to the end of the machine frame 10. The optical fibers 8 are fixed in the respective spindles, and the other ends 11 are trued up. Light is then projected from a light source 12 on the trued ends 11, and receptors 13 are provided in the respective spindles and connected to a data logger 14 at the end of the machine frame 10 with an electric wire, or light receiving optical fibers 15 are provided in the respective spindles. One end 16 of each optical fiber 15 is placed opposite to the yarn 6, and the other end is led to a receptor 17 to receive the light.