To reduce the transmitting capacity of a radar scan transmitter without deteriorating the quality of video pictures.

A scan converter 14 inputs radar video signals 16 and outputs radar video data 25. A radar display device 11 displays the data 25 and graphic data in a superimposing state. A TV timing generator 13 generates timing signals 26 and a coordinate transformer 1 performs coordinate transformation. Frame memories 2 and 4 store data and a data comparator 7 compares radar video data 18 and 21 with each other and outputs a compared output signal 22. An encoder 8 encodes the output signal 22 of the comparator 7 and outputs encoded data 23 and a transmission memory 9 stores the data 23. A transmitting timing generator 10 outputs a reading-out timing signal 24 and a D/A converter 5 converts the radar video data 18 into analog video data 19. A TV monitor 6 for maintenance monitors radar videos.