1. A system for modeling a circuit, the system comprising: a circuit simulator program stored on a computer-readable storage medium, and a computer, the circuit simulator program comprising instructions causing the computer to execute the circuit simulator program by preparing an electrical equivalent circuit as an analytic model for analyzing electrical equipment including a coil as an electrical circuit element by analyzing an operation of said electrical equipment by use of said electrical equivalent circuit concerning said analytic model, wherein said coil included in said electrical equipment is expressed by said equivalent circuit based on an inductance component, said equivalent circuit expressing said analytic model for said electrical equipment, and said inductance component being expressed by said equivalent circuit, said equivalent circuit comprising: a current source, a voltage extracting means for extracting voltage across terminals of said current source, a current generating means for determining a value of the current of said current source based on the value of said extracted voltage extracted from said voltage extracting means, said extracted voltage value to be input to said current generating means fluctuating in calculation, and a current generating means for determining a value of the current of said current source based on the value of said extracted voltage extracted from said voltage extracting means, said extracted voltage value to be input to said current generating means is fluctuating in calculation, and wherein said inductance component of said coil provides a variable inductance device connected to said current source, said voltage extracting means and said current generating means eliminate an inductance value calculation failure caused by said current-carrying path.