To provide a quadrature modulator and amplitude error control method for the quadrature modulator in which deterioration in a receiver side code error rate is improved by detecting an amplitude error signal from demodulated base band I phase signal and Q phase signal obtained through the quadrature modulator and using two amplitude correction devices, the quad rature modulator and two amplitude correction device and a quadrature demodulator so as to control the amplitude error signal thereby making the I phase signal and the Q phase signal in a quadrature modulation wave and a quadrature demodulation wave to be identical to each other.

The base band I phase signal and Q phase signal are given to input terminals 11, 12 and outputted to a quadrature modulator 30 via modulation signal amplitude correction devices 121, 122. The quadrature modulation wave outputted from the quadrature modulator 30 is partly fed back and inputted to a demodulator input selection switch 140, which selects the wave together with a reception signal inputted from other communication equipment and outputs the selected signal to an quadrature demodulator 40.