Part of a first signal path for amplifying a signal includes circuits for detecting a signal, and a second signal path connected to an input portion of the first signal path includes circuits for detecting the signal. A signal strength detector circuit adds outputs from the respective detector circuits in the first and second signal paths. The first signal path has a function of expanding the dynamic range in a smaller signal region as compared with the second signal path, while the second signal path has a function of expanding the dynamic range in a larger signal region as compared with the first signal path. When a radio transmitted output is variably controlled in a radio transmitter section based on a field strength detection output for a received signal, the transmitted output is optimized, resulting in minimizing consumed power and unnecessary radiation of radio waves.