To provide an overvoltage protecting circuit having resistance against an input voltage of inverse polarity.

A drain of a first transistor M1 is connected to an input terminal 102, and its back gate is connected to its source. A first resistor R1 is provided between the gate and the source of the first transistor M1. A second resistor R2 is provided between the gate of first transistor M1 and a reference voltage terminal 106. A first zener diode ZD1 is arranged between the gate and the source of first transistor M1 such that the cathode faces the source side. Relating to a second zener diode ZD2, its cathode is connected to an anode of the first zener diode ZD1. A third resistor R3 is provided between the anode of the second zener diode ZD2 and the reference voltage terminal 106. A second transistor M2 is provided between the cathode of the second zener diode ZD2 and an output terminal 104.

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