A first envelope detector circuit and a second envelope detector circuit are the same in circuit configuration, where the former detects an input high frequency signal, and the latter generates a reference voltage for power level detection. A detector detects an output voltage of a selector configured to select an output of the first envelope detector circuit with reference to an output voltage of a selector configured to select an output of the second envelope detector circuit. A controller controls an input selector to determine and store control values for the two selectors during input of a high frequency reference signal generated by a high frequency reference signal generating unit, and controls the two selectors by using the stored control values when an actual high frequency signal is input.