A signal transmitting apparatus includes a signal distributor, a frequency converter, and a frequency synthesizer. The signal distributor is configured to baseband signals corresponding respectively to a plurality of frequency band. The frequency converter is configured to convert each of the distributed baseband signals into one of a positive frequency signal and a negative frequency signal according to the frequency band. The frequency synthesizer is configured to synthesize the positive frequency signal and the negative frequency signal to generate a transmission signal. Herein, the positive frequency signal and the negative frequency signal are signals included in one predetermined intermediate frequency band.