To provide a protective circuit and a protector which are capable of protecting communication equipment and the like from abnormal voltage such as lightening surge in a short time, and make it possible to easily recognize that protective operation has been performed.

The thermal fuse 11, arrester 13 and protective resistor 15 of a protector 10A are placed in a centralized manner and covered with a heat-shrinkable tube 20 which has not shrunk yet. One end of the heat-shrinkable tube 20 is closed on a board 18, and the other end positioned at upper level is open. For the reason, heat generated from the protective resistor 15 and the like during normal operation is liberated through the open end of the heatshrinkable tube 20. If any abnormal voltage is applied to communication lines L1, L2, the temperature abruptly rises in the heat-shrinkable tube 20, and the heat-shrinkable tube 20 is shrunk. As a result, the temperature of the thermal fuse 11 abruptly rises and is blown in a short time, and thus a communication circuit 3 is protected from the abnormal voltage. Once the heat-shrinkable tube 20 shrinks, that shape of the tube is maintained, and it is easily recognized that protective operation has been performed.