Yarn detection device can identify whether the yarn is broken or calculate the traveling length of the yarn, so as to provide more reliable control during processing

A yarn detection device includes a yarn winder, a tension controller, and a sensor. The yarn winder is configured to stretch a yarn for winding it on the tension controller. The tension controller has a rod body that penetrates out of the surface of the tension controller, and a tension wheel is disposed on the rod body. The tension controller has a fixed rod erected at the front and rear positions of the rod body, and the fixed rod is disposed with a rotating wheel. The rotating wheel can guide the yarn to be stably wound on the tension wheel, and the yarn detection device can measure the tension value of the yarn. A sensor is mounted on the fixed rod, and a detection wheel is disposed at the bottom of the rotating wheel on the fixed rod. There is a sensing groove runs through the sensor, and the detection wheel is located within the sensing groove. The sensor senses the rotation speed of the detection wheel to identify whether the yarn is broken or the traveling length thereof.