PURPOSE: To ensure the accurate recording and reproduction of a digital data by means of a general-purpose tape recorder, by adding a data signal and an auxiliary signal together with the weighting of a prescribed ratio.

CONSTITUTION: The data signal Pa and auxiliary signal Pb are delivered through output terminals 6a and 6b of an output port 6. The signal Pb has the same logic as the signal Pa when the original data read out of an RAM4 has the logic H and vice versa when the original data has the logic L. Then both signals Pa and Pb are weighted with a prescribed ratio and supplied to an adding means 9 to be converted into the signal Pc. For this added value, the amplitude has a prescribed ratio when the data has the logics L and H respectively. Therefore the coincidence is obtained between the positive and negative areas within a period of the signal Pc for every period. Thus a normal waveform is obtained although the signal Pc is supplied to an output terminal 14 through a DC blocking capacitor 13.