To reduce the leak current in the MOSFET connected between the pad and the ground. There are provided a pad PAD for an input or output signal, an n-type MOSFET M1a connected between the pad PAD and the ground and having its gate terminal and backgate connected in common, and a potential control circuit 10 that controls a potential Vb of the gate terminal and the backgate of the n-type MOSFET M1a based on a potential Vin of the pad PAD. The potential control circuit 10 comprises n-type MOSFETs M2 and M3; the n-type MOSFET M1a has its gate terminal and backgate connected to backgates and drains of the n-type MOSFETs M2 and M3; the n-type MOSFET M2 has its source grounded and its gate terminal connected to the pad PAD via a resistance R; and the n-type MOSFET M3 has its source connected to the pad PAD and its gate terminal grounded.