PURPOSE: To eliminate substantially beat noise with a simple circuit constitution by providing a jitter mixing means to apply FM modulation to a control clock thereby adding substantially jitter.

CONSTITUTION: A bit clock from an input terminal 2 is fed to a jitter mixing circuit 30, where the clock is FM-modulated and jitter is added. The bit clock added with the jitter is fed to the clock terminal of a flip-flop circuit 31 to add substantially jitter to a digital data, a converting instruction and a word clock delivered from the flip-flop circuit 31 to a D/A converter 5 sequentially when the bit clock is applied. Thus, the data and the clock applied from input terminals 1∼4 are added with jitter to move momentarily the frequency and the beat spectrum is made spread in white noise form to eliminate substantially the beat noise.