An amplifier includes a separating unit, a generator, first to fourth switching amplifiers, and an outputting unit. The separating unit separates a pulse signal into a first separated pulse signal and a second separated pulse signal. The generator generates first to fourth low speed pulse signals by using the first and the second separated pulse signal. The first switching amplifier amplifies the first low speed pulse signal. The second switching amplifier amplifies the second low speed pulse signal by using the output of the first switching amplifier as a power-supply. The third switching amplifier amplifies the third low speed pulse signal. The fourth switching amplifier amplifies the fourth low speed pulse signal by using the output of the third switching amplifier as a power-supply. The outputting unit combines and outputs the first and the second output pulse signal.