PURPOSE: To constitute a system saving a memory or a transmission time by compressing data, accumulating and transmitting the compressed data and developing the compressed data and displaying the developed data in case of controlling a display element of a road information display device.

CONSTITUTION: The on-and-off information of respective dots in a dot matrix constituting the display surface of the display device is collected in each horizontal or vertical line, and when all dots in a line have the same value (e.g. '0'), a value '0' is applied by one bit to represent the value of the line. If the other value ('1') exists in the line, one bit is added to the head of the line, '1' is applied to the leading bit, the on-and-off information of the line is displayed following the leading bit, one bit of the final part of the compressed data is set up to '1', and the prescribed number of '0's is arranged following the final '1'. Consequently, the volume of data to be used for road information display can be compressed and deleted up to 50W70%, so that the contents of the memory necessary for a central control device can be reduced and the line occupation time for transmitting communication to a remote display device can be compressed and deleted.