PURPOSE: To display a radar video on a screen of a control scope without degrading resolutions by lowering a data rate to compress a frequency band thereof equivalently.

CONSTITUTION: First, a video data memory 1 stores a radar video 6 by the sample interval unit and an amplitude comparison circuit 2 comparrs an amplitude value with a reference amplitude value 7. Here, the reference value 7 is a video amplitude value to provide a brightness visually recognizable with a control scope. Video data above the reference value 7 is extracted with a high fidelity while one below the reference value 7 is extracted by sampling at a long interval to ignore the data in the midway with a reduction in the amount of the data. Then, a speed conversion circuit 5 converts a sample video data 10 with two different kinds of sample intervals mixed into a data with a fixed interval to be transmitted to a communication channel. Thus, fidelity of information exceeding the reference value 7 is maintained thereby enabling compression of band without degrading resolutions of the radar video.