The utility model relates to a signal testing device, including the casing, be connected with transmitting terminal, receiving terminal and transmission fiber on the casing, transmission fiber sets up between transmitting terminal and receiving terminal, is connected with the cable on the transmitting terminal, is equipped with the transcoding chip in the transmitting terminal, and cable outgoing letter number becomes audio information and sends to the receiving terminal through transmission fiber through transcoding chip transcoding, is equipped with the receipt chip in the receiving terminal, and receipt chip received signal distinguishs the quality of signal, the utility model discloses an advantage: become audio information through the transcoding chip in the transmitting terminal with cable outgoing letter transcoding to send audio information to the receiving terminal through transmission fiber, distinguish through the receipt chip received signal in the receiving terminal and to the signal, the quality of can be quick clear resolution signal, the rate of accuracy is high, and work efficiency is high.