To eliminate the need for a compounder and a dedicated A/D converter for a transmission power monitor signal and render a normal observation and a transmission power monitor by a method, wherein a switch is provided for selecting an attenuator dedicated to the observation and an attenuator dedicated to the transmission power monitor.

A reception signal 6 passes a first switch 9 which selects a side of a normal observation attenuator and attenuates a predetermined reception signal level in a normal observation attenuator 10. This signal passes a second switch 11 which selects a side of the normal observation attenuator 10, is amplified by a reception amplifier 13, and is converted into a video by a frequency converter 14. Next, the converted signal is A/D-converted and converted into predetermined observation data with a signal processor 16. When it is transmission power monitor, a monitor signal passes the switch 9 set at the side of a transmission power monitoring attenuator 12 and is attenuated by the attenuator 12. After this signal passes a switch 11 and is amplified by a reception amplifier 13, it is converted by a frequency converter 14 and then is A/D-converted, thereby converted into predetermined observation auxiliary data by the signal processor 16.