N (integer equal to or above 3) quaternary phase shift keying (QPSK) outputs having different amplitude levels, i.e., r2=r1×2−(i−1), i=2 . . . N with respect to a maximum amplitude level r1 are superposed after power amplification to form M(=22N)-valued/quadrature amplitude modulation (QAM), and N-1 outputs si except the quaternary phase shift keying QPSK-1 having the maximum amplitude r1 are subjected to power amplification in this formation, then the outputs are combined by a directional coupler to obtain a combined signal, and an output of the quaternary phase shift keying QPSK-1 and the combined signal are transmitted from two systems of antennas to be vectorially superposed and combined in a space.