PURPOSE: To observe wave information accurately and easily by observing a sea clutter from waves of the sea, and displaying the evaluated class of waves quantitatively from the extent of a sea clutter signal.

CONSTITUTION: A reflected wave from waves which is received by a radar antenna 1 is led to a radar indicating machine 3 through a logarithmic linear receiving circuit 2 and also led to a constantamplitude wave signal amplifying circuit 5 through an azimuth and distance gate circuit 4 at the same time. The azimuth and distance gates of the gate circuit 4 are set with an azimuth dial 7 and a distance gate dial 8 provided to an operating device 6. The operating device 6 is further provided with a wave scale dial 9 and a wind-force scale dial 10. The circuit constant of the amplifying circuit 5 is adjusted and set associatively with both dials 9 and 10. A wave signal from the amplifier 5 is led to a distance and amplitude display device 13. The dials 9 and 10 are so adjusted that the wave signal is constant, and the wave scale wind-force scale are read on their dial scales.