There is provided a playback method for decode-processing and playing back coded audio data which is transmitted with necessary stereo process information required for a stereo process intermittently multiplexed into coded information of a monaural audio signal. The playback method includes a first step of outputting stereo audio signals using the monaural audio signal if the necessary stereo process information is not supplied; a second step of starting updating stereo variables within filters, and outputting the stereo audio signals using the monaural audio signal until all the state variables are updated, if the necessary stereo process information is supplied; and a third step of performing the stereo process based on stereo process information acquired by the necessary stereo processinformation, on the monaural audio signal to generate and output stereo audio signals, if all the state variables within the filters are updated. The invention is applicable to the voice processing field.