The present invention relates to an input and output port circuit. The input and output port circuit comprises a signal register for storing output signals, an input/output register at which an input/output control signal for determining an input/output direction is stored, a plurality of control registers, a power supply switch circuit for selectively supplying a low voltage or a high voltage depending on a power mode control signal, a signal direction control circuit for determining the direction of the signal depending on a value of the signal register and a value of the input/output register, an output control circuit driven depending on the value of the control register and an output of the signal direction control circuit, and an output driving circuit for outputting the low voltage, the high voltage or the ground value depending on an output of the signal direction control circuit and an output of the output control circuit. The high voltage and the low voltage can be simultaneously driven using only a single output driving circuit and the single output driving circuit is constructed in multiple stages and is selectively driven by the output control register. Therefore, the power consumption can be saved.