Control side equipment and at least one equipment under control are commonly interconnected via a data line and a strobe line. The equipment under control is provided with means for retaining the logic of a strobe pulse when it is received from a strobe line. When the control side equipment has set data on the data line and provided the strobe pulse on the strobe line, the logic hold means of the equipment under control holds the logic of the strobe pulse and the data set on the data line is fetched therefrom into the equipment. Thereafter, the logic hold is released to thereby inform the control side equipment that the equipment under control is ready for receiving the next data. The control side equipment monitors the strobe line and, upon detection of the information, sets new data on the data line and sends out a strobe pulse. Thereafter, similar operations are carried out, by which data are sequentially transferred from the control side equipment to the equipment under control. In the case of transferring data from the equipment under control to the control side equipment, when the control side equipment sends out a strobe pulse representing that it is ready for receiving data, the logic hold means of the equipment under control holds the logic of the strobe pulse, data is set on the data line and then the logic hold is released, by which the control side equipment is informed that the data to be transferred has been set. Upon detection of releasing of the logic hold by monitoring the strobe line, the control side equipment fetches the data from the data line and when it has become ready for receiving the next data, it sends out a strobe pulse again, thus, fetching data one after another.