Abstract: An input/output circuit (I/O circuit) includes the following elements. An input/output pad (I/O pad) has a plurality of operation mode, including an output mode, a normal input mode and a tolerance mode of an input mode. A first control circuit provides a first control signal in response to a pad voltage of the I/O pad and a supply voltage. A first P-type transistor has a first body region to receive a first control signal. A second P-type transistor has a second body region to receive the first control signal. In the input mode, when the pad voltage is lower than or equal to the supply voltage, the I/O pad operates in the normal input mode, and, when the pad voltage is higher than the supply voltage, the I/O pad operates in the tolerance mode, and voltage of the first control signal is equal to pad voltage.