A method of frequency analysis is introduced on a basis of the Fourier integral, and is applied to certain types of atmospherics: (1) the atmospherics radiated from return streamer of lightning flash in the day time, (2) the quasi sinusoidal waveform at night. The results obtained by this method show that: (1) the distance effects with relation to the spectrum of not only the complete waveform, but also each quasi one-cycle of the waveform, (2) the decreasing effects of the latter spectrum accompanied by the increasing order number of the quasi one-cycle in waveform. In the latter part of this paper, one waveform, having two large maximum values in higher frequency region in the amplitude frequency spectrum, is given and investigated in relation to a feature of the waveform.