Protection device and protection method

In a first transistor (TR1), a current path is connected in series to a communication wire. When the current through the current path of the first transistor (TR1) becomes greater than or equal to a set current, a current limiting control unit (231) limits the current through the current path by controlling the first transistor (TR1) to increase the resistance of the current path. When the voltage between the two ends of the current path of the first transistor (TR1) becomes greater than or equal to a set voltage, a load limiting unit (232) switches the first transistor (TR1) off.