PURPOSE: To transmit various kind of information besides information showing that where is a body at a reflection point, by constituting to vary the reflectivity of a reflecting plate according to the information to be transmitted.

CONSTITUTION: For example, when an input signal to an input circuit 6 is a velocity signal (a) of a vessel, etc., the velocity signal (a) is encoded by an encoding circuit 5 and passed through a waveform shaping circuit 4 and a modulator 3 to turn on and off a reflecting plate 2. If a pulse wave of a radar arrives as shown by an arrow A, when it is modulated by the signal (a), a reflected radio wave is code- modulation in the form of the encoded signal (a). For this purpose, waveform shaping is performed after the detection of rader-side receiver through a holding circuit fitted with reset peak or a low-pass filter to reproduce a wave, modulated at a reflection terminal side, at the rader side. Thereby transmitting the speed signal (a) to the rader side. Thus, various kind of information are transmitted in addition to information showing that there is a body at the reflection point.