A sub-scrambling/descrambling method and device enhances the degree of scrambling of linear PCM data. Data is delimited at predetermined times, and the minimum value of a run is found and used as annex information. The run part is replaced with an arbitrary irreversible random data string, which is processed by a main scrambling device to generate transmission data. After main descrambling of the transmission data, a descrambling device takes out the annex Information and replaces the random data string with a predetermined "0" or "1" run according to the annex information. Thus, the degree of scrambling of linear PCM data is enhanced as much or more than compressed video data.