To provide a method of scrambling/descrambling analog signals application to international telephones or short-wave radio communications, etc., having sufficient encryption strengths and also applicable to inferior in line quality.

The method of scrambling/descrambling analog signals uses FIR filters for conducting linear convolution, delay means, constant generating means, adder and multiplier. The constant generating means outputs other than 0 and its absolute value is less than 1. The FIR filter used in either scrambling or descrambling process has filter coefficients h, obtained by a specified discrete Fourier transformation and the other FIR filter used in the other process has filter coefficients inverted in series to the filter coefficients h of the one FIR filter on the time axis.