In substrate noise analysis for a semiconductor integrated circuit, it takes long to calculate the amount of current input to the substrate and substrate potential fluctuations in an analog circuit to which the current is propagated in combination with impedance/power supply resistance of the substrate including a large scale RC circuit network. The amount of calculation is reduced in calculating current passed to power supply/ground by adding triangles having areas corresponding to power consumption separately for rising/falling in logical changes in gate level simulation. The amount of calculation is reduced by summing current, interface capacitance, interface resistance, power supply resistance, ground resistance, power supply voltage fluctuations, and ground voltage fluctuations on a basis of block, instance or simultaneous operation. Since the calculation amount is reduced, it takes a shorter period to apply substrate noise analysis. In addition, the elements for calculation are also reduced, and therefore substrate noise analysis can be applied to a large scale semiconductor integrated circuit.