PURPOSE: To minimize the delay of a signal and reduce the scale of hardware to simplify reproducing control procedures, by making the frequency of a reproducing signal coincident with the frequency of a transmission clock signal source practically.

CONSTITUTION: Input data 21 to a transmitting station 1 is sampled in an input circuit 3 by a clock f0 and is transmitted as a frequency f1 from a transmitting circuit 4. In a receiving station 2, data is sampled in a receiving circuit 5 by a clock f2 and is stored in a register 6. The number of data in the register 6 is supplied to a discriminating circuit 8 and is compared with thresholds TH and TL, and data is reproduced in accordance with the number of data by clocks fH and fL. At this time, a switching circuit 9 selects a signal source 14 of the clock fH when the number of data is larger than the threshold TH, and the circuit 9 selects a signal source of the clock fL when the number of data is smaller than the threshold TH. As the result, reproduced data 23 is obtained from an output circuit 7.