An overcurrent protecting device for protecting a semiconductor element from an overcurrent, comprising: the semiconductor element; a shunt resistor for detecting an electric current flowing through the semiconductor element, wherein the shunt resistor detects the overcurrent when the electric current in the semiconductor element exceeds a threshold value; a driving circuit for operating the semiconductor element; a reference resistor for setting the threshold value for starting a protecting operation with respect to the overcurrent; a constant electric current circuit for supplying a constant electric current to the reference resistor; and a comparator for comparing a terminal voltage of the shunt resistor and a terminal voltage of the reference resistor, wherein the shunt resistor is made of a same kind of resistor as the reference resistor; characterized in that the semiconductor element is adapted to output a signal to a communication line in order to communicate with an electronic device mounted on an automotive vehicle, the semiconductor element is a bipolar transistor, the driving circuit provides a base potential to the NPN semiconductor element, the driving circuit includes a limiter circuit and an output side NPN transistor, the emitter of which is connected with the base of the semiconductor element, the limiter circuit includes a plurality of bipolar transistors (52, 54, 55, 57), wherein one end of two series diode-connected NPN transistors (54, 55) of the plurality of bipolar transistors (52, 54, 55, 57) is connected to a current source and to the base of a PNP transistor of the plurality of bipolar transistors (52, 54, 55, 57), and the other end of the series diode-connected NPN transistors (54, 55) is connected to ground, the collector of the PNP transistor is connected to ground, and the emitter of the PNP transistor is connected to the base of the output side bipolar transistor, the emitter of the output side bipolar transistor is further connected with a resistor having its other terminal connected to ground, the plurality of bipolar transistors (52, 54, 55, 57) further includes an NPN transistor having an emitter connected to ground, and a collector connected to the one end of the of two series diode-connected NPN transistors (54, 55) and to the current source. the semiconductor element; a shunt resistor for detecting an electric current flowing through the semiconductor element, wherein the shunt resistor detects the overcurrent when the electric current in the semiconductor element exceeds a threshold value; a driving circuit for operating the semiconductor element; a reference resistor for setting the threshold value for starting a protecting operation with respect to the overcurrent; a constant electric current circuit for supplying a constant electric current to the reference resistor; and a comparator for comparing a terminal voltage of the shunt resistor and a terminal voltage of the reference resistor, wherein the shunt resistor is made of a same kind of resistor as the reference resistor; characterized in that the semiconductor element is adapted to output a signal to a communication line in order to communicate with an electronic device mounted on an automotive vehicle, the semiconductor element is a bipolar transistor, the driving circuit provides a base potential to the NPN semiconductor element, the driving circuit includes a limiter circuit and an output side NPN transistor, the emitter of which is connected with the base of the semiconductor element, the limiter circuit includes a plurality of bipolar transistors (52, 54, 55, 57), wherein one end of two series diode-connected NPN transistors (54, 55) of the plurality of bipolar transistors (52, 54, 55, 57) is connected to a current source and to the base of a PNP transistor of the plurality of bipolar transistors (52, 54, 55, 57), and the other end of the series diode-connected NPN transistors (54, 55) is connected to ground, the collector of the PNP transistor is connected to ground, and the emitter of the PNP transistor is connected to the base of the output side bipolar transistor, the emitter of the output side bipolar transistor is further connected with a resistor having its other terminal connected to ground, the plurality of bipolar transistors (52, 54, 55, 57) further includes an NPN transistor having an emitter connected to ground, and a collector connected to the one end of the of two series diode-connected NPN transistors (54, 55) and to the current source.