PURPOSE: To perform the stable orthogonal modulation of complex signals with simple construction.

CONSTITUTION: The polarity of a real part signal I of a digital complex signal is inverted by a polarity inversion circuit 64. The polarity of an imaginary part signal Q of the digital complex signal is inverted by a polarity inversion circuit 65. Signals I, Q, -I, and -Q are inputted to a switch circuit 63. The switch circuit 63 is switched by sampling frequency fs, and the complex signals I, Q, -I, -Q,... are successively outputted at the timing of sampling frequency fs. This is D/A-converted by a D/A converter 68, and the carrier wave frequency fIF component is taken out. The relation between the sampling frequency fs and the carrier wave frequency fIF satisfies fIF=fs (2n+1), the orthogonal modulation signal can be easily obtained.