In a calculation apparatus for calculating intensity of an electromagnetic field radiated from an electronic circuit device, the apparatus includes: an input data file for storing structural information of the device; an input unit for receiving structural information of the device to be analyzed from the input data file; a section unit for dividing the device into applicable sections for a distributed constant circuit method and inapplicable sections for the method by analyzing the structural information of the device; a first calculation unit for calculating current distribution at the applicable sections using the distributed constant circuit method; a second calculation unit for calculating current distribution at the inapplicable sections using a moment method and using the current distribution obtained by the first calculation unit; a third calculation unit for calculating the intensity of electromagnetic fields radiated from the device based on the current distributions obtained from the first and second calculation unit; and an output unit for outputting the calculated intensity of the electromagnetic fields to an output data file.