Abstract: A scheme for judging an active/dead status of a communication cable, which is capable of making an accurate judgement quickly for each cable laid at a working site. In this scheme, data representing a frequency spectrum of signals on a communication cable measured in a state in which the communication cable is known to be active/dead is stored in advance, and the data representing the frequency spectrum of the signals on a communication cable to be judged is measured by detecting signals on the communication cable to be judged while electromagnetically coupling a probe to the communication cable to be judged. Then, the active/dead status of the communication cable to be judged is judged according to a result of comparing a prescribed threshold with a difference of the data representing the frequency spectrum stored in advance and the data representing the frequency spectrum measured by the probe.