PURPOSE: To eliminate the interference image of circular type caused between the radar units equal in transmission repetitive frequency, by random generation of trigger pulse for transmission repetition.

CONSTITUTION: The oscillation frequency of the crystal oscillation circuit 3 is frequency divided 4 to obtain the trigger pulse for repetitive transmission and the distance marker pulse. Further, the frequency divided output for trigger pulse produces the trigger pulse having random period by using the random time circuit 7 and the modulation oscillation circuit 8. Thus, the synchronous interference image of circular type produced between the radar units equal in the repetitive frequency is taken as asynchronous interference image and this interference image is eliminated when required.