PURPOSE: To transmit a correspondent signal without fail even when the pulse width of a receiving signal is small by providing a continuous wave CW amplifier together with a pulse amplifier and operating this CW amplifier before the arrival forecasting time of the receiving signal.

CONSTITUTION: When a CW amplifier 8 can be operated before the arrival forecasting time of a receiving signal (a), transmission can be executed immediately when the signal is received. When the signal is received, a signal is outputted by an input detecting circuit 5 and a pulse amplifier 2 is caused to be in an operating condition by a signal from a control circuit 6. Then, the transmission is executed. After that, the CW amplifier 8 is controlled to a stop condition so that the phases of the output of the pulse amplifier 2 and the output of the CW amplifier 8 can not go to be reverse next and an output level can not be lowered. Thus, even when the pulse amplifier of a large output is used, the transmission can be executed without time delay and a response can be executed even to the signal of the short pulse width.