PURPOSE: To constitute a retro directive transmitter-receiver applying conventional phase synthesis by providing plural amplification sections having an interface in terms of a frequency so as to prevent the oscillation of a IF, band amplifier due to leakage from a power supply line or the line.

CONSTITUTION: Plural amplifier sections having a frequency interface comprising plural down-converters 6a-6e in an input signal processing path, plural oscillators 7a, 7b and plural IF band amplifiers 9a, 9b. After phase synthesis processing by a 2-multiplier and up-converters 13a-13d is implemented, the frequency conversion is applied with the same oscillators as those used for a local signal of the down-converters 6a-6c, and IF band amplifiers 9a, 9b and up-converters 13a-13d the same number as that of the down-converters 6a-6c. Thus, even to a pilot signal with a small reception level, the IF band amplifier is not oscillated to obtain a retro directive transmitter-receiver able to attain conventional phase synthesis processing.