PURPOSE: A digital modulation device and a method thereof are provided to generate a pseudo-digital signal for driving a class-s power amplifier entirely in a digital domain. CONSTITUTION: A first low-pass delta-sigma modulator(121) outputs a first signal by delta-sigma modulating the size of a baseband signal. A second low-pass delta-sigma modulator(122) outputs a second signal by delta-sigma modulating the phase of the baseband signal. A multiplexer(125) selects one carrier pulse signal among multiple carrier pulse signals with multiple discrete phases according to the second signal and outputs the carrier pulse signal. A logical product device(126) generates a pseudo-digital signal by using one carrier pulse signal and the first signal.