An amplifying device for amplifying an input audio signal input to the amplifying device to output a sound, the amplifying device comprising: a signal delay processor operable to output the input audio signal with a predetermined time of delay; an amplifier operable to amplify a signal output from the signal delay processor; a voltage variable power supply operable to supply an output voltage to the amplifier; and a supply voltage controller operable to output a supply voltage control signal to the voltage variable power supply to control the output voltage of the voltage variable power supply, a read-ahead update unit operable to generate a read-ahead signal indicating a constant time, and to update the constant time, wherein the supply voltage controller is operable to calculate an envelope of the input audio signal from the input audio signal to generate the supply voltage control signal so that a waveform of the supply voltage control signal follows a waveform of the envelope, and to output the supply voltage control signal to the voltage variable power supply, at a rising edge of the supply voltage control signal, said supply voltage control signal is output prior to the predetermined time by the constant time, at a falling edge of the supply voltage control signal, said supply voltage control signal is curved along the envelope, and the read-ahead update unit is operable to update the constant time on the basis of a comparison between the envelope and the output voltage from the voltage variable power supply by decreasing the constant time when the output voltage of the voltage variable power supply is greater than the envelope and increasing the constant time when the output of the voltage variable power supply is less than the envelope. a signal delay processor operable to output the input audio signal with a predetermined time of delay; an amplifier operable to amplify a signal output from the signal delay processor; a voltage variable power supply operable to supply an output voltage to the amplifier; and a supply voltage controller operable to output a supply voltage control signal to the voltage variable power supply to control the output voltage of the voltage variable power supply, a read-ahead update unit operable to generate a read-ahead signal indicating a constant time, and to update the constant time, wherein the supply voltage controller is operable to calculate an envelope of the input audio signal from the input audio signal to generate the supply voltage control signal so that a waveform of the supply voltage control signal follows a waveform of the envelope, and to output the supply voltage control signal to the voltage variable power supply, at a rising edge of the supply voltage control signal, said supply voltage control signal is output prior to the predetermined time by the constant time, at a falling edge of the supply voltage control signal, said supply voltage control signal is curved along the envelope, and the read-ahead update unit is operable to update the constant time on the basis of a comparison between the envelope and the output voltage from the voltage variable power supply by decreasing the constant time when the output voltage of the voltage variable power supply is greater than the envelope and increasing the constant time when the output of the voltage variable power supply is less than the envelope.