A squaring circuit squares a radio transmission signal. A band-pass filter extracts
a spectrum component corresponding to a desired channel, from that low-frequency
component of the output of the squaring circuit, which occurs with a center thereof
being present near a DC (Direct Current). A level measuring circuit measures the
level of the extracted spectrum component. On the other hand, another band-pass
filter extracts, from the output of the squaring circuit, a spectrum component
corresponding to spectrum spreading due to a distortion in a transmission circuit.
Another level measuring circuit measures the level of this extracted spectrum component.
A level radio measuring circuit measures a ratio between the level measured by
the level measuring circuit and the level measured by the other level measuring
circuit, and produces the measured result as a ratio of a leak power to an adjacent channel.
