A delayed input signal from a delay circuit (24) and an output signal are combined by a combiner (51). The output form combiner (51) is converted into a low-frequency signal by a frequency converter (53). Distortion components are extracted from the output from the frequency converter (53) and measured by a power detector (55). A control circuit (56) controls a second vector controller (11) in a distortion cancel loop (102) to minimize the measured distortion components.
