An electromagnetic field intensity calculating device calculates according to a moment method the intensities of the electric field and the magnetic field radiated by an electric circuit device having metal portions and dielectric portions. The electromagnetic field intensity calculating device comprises an input unit for inputting the precise structure of the electric circuit device including the structure of the metal portions and the structure of the dielectric portions; a deriving unit for deriving simultaneous equations based on the structure of the electric circuit device input to the input unit, a calculating unit for calculating the electric current flowing through the metal portions and the equivalent electric current and the equivalent magnetic current flowing through the dielectric portions by solving the simultaneous equations; and a computation unit for calculating the intensity of the electric field and the magnetic field radiated by the electric circuit device based on calculation results obtained by the calculating unit.