Solving simultaneous equations of the moment method defining relationships between a mutual impedence between elements of an electronic apparatus, a wave source, and an electric current flowing in each element so as to simulate an electric current, provided with a unit for calculating the mutual impedance at a sampling frequency and calculating approximation coefficients, when expressing the mutual impedance by approximation expressions in terms of exponents and exponent powers, from the calculated values and sampling frequency; a unit for forming the simultaneous differential equations by setting the approximation coefficients and initial value with respect to the simultaneous differential equations derived by performing a Fourier transform on the simultaneous equations of the moment method in which the approximation expressions are substituted; and a unit for calculating the electric current in the time domain flowing through the specified element by solving the simultaneous differential equations formed.