PURPOSE: To obtain operation conditions which are not affected by a load capacity or the like and accelerate the convergence of simulation, by satisfying relations, which are determined by prescribed expressions, among respective parameters such as the load capacitor in a voltage comparing circuit.

CONSTITUTION: An FF consists of a transistors TRs 3 and 4, which are cross- connected and are loaded with storage batteries 1 and 2, and a circuit 5 which lowers the source potential of this FF. In a voltage comparing circuit where the source potential of this FF is decreased gradually from a potential approximating the potential, where storage batteries 1 and 2 are charged, to output a logical state corresponding to the magnitude in the initial state, parameters of a load capacity CL, a gate/source capacity Cgs of MOS TRs 3 and 4, a gate/ drain capacity Cgd, a gate/channel capacity Cch, an initial potential difference ΔV0, an effective channel length L of TRs, a width W of them, a gate oxide film capacity C0X per unit area, a carrier movement degree μ, a variance allowable value ΔVT of the threshold voltage, and a voltage drop speed u1 are set to satisfy relations determined by expressions.