A signal transmitting apparatus includes: a first converting device arranged to generate an up-converted in-phase signal according to an in-phase digital signal and a first pre-distortion signal; a second converting device arranged to generate an up-converted quadrature signal according to a quadrature digital signal and a second pre-distortion signal; an amplifying device arranged to generate an amplified signal according to the up-converted in-phase signal and the up-converted quadrature signal; and a processing device arranged to generate the first pre-distortion signal according to a first combination signal combined by a cube of the in-phase digital signal and a multiplication of the in-phase digital signal and a square of the quadrature digital signal, and to generate the second pre-distortion signal according to a second combination signal combined by a cube of the quadrature digital signal and a multiplication of the quadrature digital signal and a square of the in-phase digital signal.