AbstractIn a discharge between charged metal spheres, the effect of the metal spheres on the generated electromagnetic field has not been clearly indicated. One of the authors (Fujiwara) has proposed the following computation method (called the image dipole method) for a spark discharge between metal spheres. The surface of the metal sphere is replaced by an infinite number of image charge pairs, which are arranged so that the surface is kept at the same potential. Then, the generated electromagnetic field is calculated analytically by superposition of the dipole fields caused by the spark current derived from the Rompe‐Weizel spark‐resistance law. It has been shown by the analysis that the metal sphere increases the field level. Then, the electromagnetic field generated by the spark discharge between metal spheres is calculated numerically by the finite‐difference time‐domain (FDTD) method, with the spark current as an excitation source for the metal sphere. The validity of the approach has been shown through comparison to the analytic solution by the image dipole method for the magnetic field waveform.However, the above computation method has the problem that the static electric field before the onset of the discharge cannot be calculated, which makes it difficult to understand fully the ESD field produced by the charged metal bodies. In this paper, the generated electromagnetic field is calculated by the FDTD method (voltage source method), with the spark voltage derived from the spark‐resistor law as an excitation source. The result is compared to the results of calculations by the image dipole method and the current source method. It is shown that the waveform of the electrostatic field cannot be calculated by the current source method, but the voltage source method can calculate the field as in the case of the image dipole method. It is also seen that the magnetic field waveforms obtained by any calculation almost completely agree. The magnetic field waveform generated in the discharge experiment between metal spheres is observed by using a shielded magnetic field probe and a wideband oscilloscope (bandwidth 1.5 GHz), and is shown to agree almost completely with the results of calculations by the voltage source method and the image dipole method. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 86(7): 54–63, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.1169