PURPOSE: To eliminate the power consumption on the common bus in case the common bus does not attain its original function, by providing the current supply capacity selectively only when required to the load element of the common bus.

CONSTITUTION: The E type MOS transistor is used for each of the load elements 6a', 6b' and 6c' of the common buses A, B and C respectively. These transistors are controlled by the enable signals Ea, Eb and Ec supplied from the control part 4, and the current supply capacity is provided selectively. Thus the signals Ea, Eb and Ec are sent to the gates of the elements 6a', 6b' and 6c' of the common buses and only for the time during which the data of each common bus is effective and required. In this way, the power consumption can be eliminated on the common bus in the time during which the common bus does not attain its original function.