A coefficient computing section, for computing a characteristic reverse to an input/output characteristic of the power amplifier, is configured by a fixed coefficient storing section and an error coefficient computing section. The fixed coefficient storing section is previously stored with the characteristic reverse to a pre-measured input/output characteristic. The error coefficient computing section computes an error coefficient between a characteristic stored in the fixed coefficient storing section and a current characteristic of the power amplifier. When the determining section determines that the adjacent-channel leak current power ratio is greater than a predetermined value, an operation halt is instructed to the power amplifier.