Transmission outputs of a plurality of transmission branches (101, 102) are extracted by coupler sections (161, 162). Branch detectors (121, 122) respectively detect the levels of the extracted signals of the respective transmission branches and a combination detector (130) detects an output obtained by combining two extracted outputs from the transmission branches by a signal combining section (110). An amplitude error is detected and corrected by comparing output levels of the branch detectors (121, 122), and a phase error is detected and corrected by an output level of the combination detector (130).