A CMOS circuit characteristic automatic adjustment apparatus includes a replica signal generation circuit for generating a replica signal capable of minimizing a drain voltage of an MOS transistor in a target circuit, a replica circuit for receiving the replica signal, voltage buffers for receiving respective drain voltages of MOS transistors in the target circuit and the replica circuit, respectively, MOS transistors for receiving respective output voltages of the voltage buffers, a comparison circuit for comparing respective sizes of currents flowing in the MOS transistors, respectively, and an adjustment circuit for adjusting, based on a comparison result, operation states of the target circuit and the replica circuit.