An audio sound signal encoding device includes: a converter that adds up all multiple channel signals included in multichannel voice sound input signals to generate an addition signal and generates a difference signal between channels of the multiple channel signals; a first encoder that encodes the addition signal in a coding mode in accordance with a characteristic of the addition signal to generate first encoded data; a second encoder that encodes the difference signal in the coding mode that was used for encoding the addition signal, to generate second encoded data; and a multiplexer that multiplexes the first encoded data and the second encoded data to generate multichannel encoded data.