PURPOSE: To increase the operating speed regardless of the reading cycle of the control data by providing a priority area to a main memory of a computer to inform an electric center to a computer interface.

CONSTITUTION: A computer interface 3 reads out a priority area 7 and checks the change of a priority bit. When this change is detected, the control data 5 is read out and transferred to a master station TC2. At the same time, the interface 3 reads out the data 5 successively in a comparatively slow fixed cycle and transfers it to the station TC2. The area 7 has a bit inversion for each change of operation by a computer 4 regardless of the interface 3. While the interface 3 always reads out the area 7 and detects a change of operation. Then the interface 3 checks an electric center with an operation request and reads out the control data of the requested electric center.