In a semiconductor circuit, an impedance adjustment circuit having the characteristics same as those of a circuit having the nonlinear resistance characteristics is configured to include an operating point calculation circuit automatically calculating an operating point with a reference resistance through feedback control, and an impedance calculation circuit calculating the impedance at the operating point found by the operating point calculation circuit. The impedance adjustment circuit is also provided with an impedance determination circuit that determines whether or not the impedance found by the impedance calculation circuit is in a predetermined range. These components, i.e., the operating point calculation circuit, the impedance calculation circuit, and the impedance determination circuit, are provided each two for High-side and Low-side impedance adjustment use.