Impulsive electromagnetic noise is caused by ESD. Especially, micro gap discharge of less than 1kV produces GHz band width electromagnetic noise. It is thought ESD noise has possibility that affects to various electrical systems. Then, we investigated whether the approach speed of spherical electrodes has an influence on the amplitude of electromagnetic radiation. As the result, we concluded that the approach speed of spherical electrode was one of the parameters which decide the size of the electromagnetic radiation from this experiment. Moreover, we considered that the amplitude change with the approach speed becomes logarithm.