The present invention discloses a buffer circuit including: a pre-driver providing a first, a second, a third and a fourth driving signals according to the voltages of voltage nodes and control signals; a voltage-detection and bias circuit providing bias voltages for an output buffer and an input buffer according to the voltages of the voltage nodes and the third driving signal; the output buffer determining conduction states of the transistors of the output buffer according to the voltages of the voltage nodes, the first and the second driving signals, and the bias voltages, and thereby outputting an output signal to a signal pad; and the input buffer determining the conduction states of the transistors of the input buffer according to the voltage of the signal pad, the voltages of the voltage nodes, the fourth driving signals, and the several bias voltages, and thereby generating an input signal.