In a protection circuit of an input/output terminal I/O, three types of PNP bipolar transistors are included. In a first PNP type bipolar transistor 10A, the emitter thereof is connected to the input/output terminal I/O, the base thereof is connected to a high-potential power supply terminal VDD, and the collector thereof is connected to a low-potential power supply terminal VSS. In a second PNP type bipolar transistor 10B, the emitter thereof is connected to the input/output terminal I/O, and the base and the collector thereof are connected to the high-potential power supply terminal VDD. In a third PNP type bipolar transistor 10C, the emitter thereof is connected to the low-potential power supply terminal VSS, and the base and the collector thereof are connected to the high-potential power supply terminal VDD.