By a simple computation, orthogonal errors from an orthogonal modulator and an orthogonal demodulator are separately corrected. Based on the amplitude of a demodulated signal, an orthogonal-error detection unit (320) detects orthogonal errors from an orthogonal modulation unit (140) and an orthogonal demodulation unit (230). Specifically, according to the distribution of transmission signal points on an I-Q plane, demultiplexers (321 and 322) in an orthogonal-error detection unit (320) separate a demodulated signal into a signal on the I-axis and a signal on the Q-axis. Zero-crossing detection units (325 and 326) detect the amplitudes of the separated signals at the intersection of the I- and Q-axes. The orthogonal-error detection unit (320) detects the orthogonal errors based on results from comparing the amplitudes at said intersection. A gain control unit (330) controls settings for a transmission orthogonal-error correction unit (120) and reception orthogonal-error correction unit (250) according to the detected orthogonal errors.