A running yarn line inspection method inspects yarn lines running in parallel in the same surface. The running yarn line inspection method is provided with a first illumination means and a line sensor for imaging the yarn lines on the side of the first surface of the running surface of the yarn lines and a second illumination means on the side of the second surface, and comprises a data processing means which processes data obtained by the line sensor and a recording means which records data processed by the data processing means with time.