The invention relates to the problem of the driving of the LCD electrooptic-switching element with alternating, square-wave electric signals, the amplitude of witch can vary between different voltage levels in correspondence with the actual functioning state of the LCD electrooptic-switching element. A distance distribution image obtaining unit obtains a distance distribution image produced based a measured result output from a distance distribution measuring unit for measuring distance distribution to an object within a predetermined view field. A checksum trailer value to maintain correctness of the checksum in the data packet having the modified timestamp is determined.