Provided are a highly efficient, low waveform distortion power supply device and a power amplifying apparatus with high efficiency and high linearity using the device as a power supply.A power supply device of the present invention comprises a linear amplifier unit 400 which linearly amplifies an input signal and outputs it as an electric current Ic, and a switching amplification control unit 500, which outputs an electric current Im using a plurality of switching amplifying units 601, 602, . . . 60n for outputting respective predetermined voltages on the basis of the magnitude of the electric current Ic outputted from said linear amplifier unit 400; and it generates an output voltage Vout according to the waveform of the input signal, and outputs an electric current Iout which is a combination of the electric currents Ic and Im.