The transmission circuit includes a comparator that converts a phase-modulated signal from an orthogonal modulator into a pulse signal so as to use the pulse signal as the sampling clock of the a delta-sigma modulator, and an asynchronous clock transfer unit and an interpolating circuit, disposed between a circuit operating based on the baseband clock and the delta-sigma modulator. The asynchronous clock transfer unit converts the amplitude component signal synchronized with the baseband clock, into an amplitude component signal synchronized with an N-frequency divided clock obtained by dividing the frequency of the sampling clock by N. The interpolating circuit interpolates the output signal from the asynchronous clock transfer unit so that the amount of change of one sample in the N-frequency divided clock becomes equal to the amount of change of one sample in the sampling clock.