It possible not only to reduce a delay, but also to enhance the coding efficiency and reduce audio artifact upon coding.An audio signal coding method for coding an audio signal to be coded, the method comprising: judging for each of frames whether or not coding should be performed on each of two or more subframes into which the frame is divided, based on an audio signal contained in the frame into which the audio signal to be coded is divided for every set of samples; and when judged that the coding should be performed on each of the subframes, performing, for each subframe, subframe processing of (i) determining a value representing a characteristic of an audio signal of the subframe, and (ii) coding the audio signal using the determined value, wherein in the performing of the subframe processing, whether or not all the values determined for the subframes are the same is judged, and when all the values are the same, the audio signal is coded as exceptional processing, using a characteristic different from characteristics of audio signals indicated by the values.