An RF circuit on a circuit simulator to be used in a microwave or millimeter wave range or a high-frequency range includes a function for being inserted by a first port and a second port thereof in a circuit to be observed, at an arbitrary cross-sectional point of the circuit, and evaluating a reflection coefficient (or a characteristic impedance) in the cross-section. The insertion loss between the first port and the second port is zero or approximately zero and is ignorable also for any finite system impedance other than zero.