PURPOSE:To prevent distortion from being generated to a reception data by adding a data consecutive to just preceding and just succeeding data for a short time length to both ends of the data in the unit of a prescribed time length as one unit data. CONSTITUTION:When data D'1-D'4 added with the data consecutive to its just preceding and just succeeding data to both ends of the data in the unit of a prescribed time with a short time length are read, the data are read while being compressed on a time base by a period tsy only at every frame and the result is outputted from a D/A converting means 8 as a privacy signal. Boundary parts of the data D'1-D'4 rearranged on the time base are not continuous and distortion is generated by the limit of a frequency band for a transmission line or the like. Data DELTAdr1-DELTAdr4 are set so that the time for the distortion generation is kept within a range of the time of the data DELTAdr1-DELTAdr4 added just after the data D'1-D'4 in the unit of prescribed time.
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