A coding and decoding method for a terminal apparatus used for multipoint phone connection, the method comprising: a coding step of, for a predetermined time period, obtaining a monaural code by coding a mixed signal of input sound signals of C channels by a first coding scheme, obtaining an extension code including a code representing information corresponding to a difference between the input sound signals of C channels, and outputting the monaural code and the extension code as codes representing the sound signals of C channels, C being an integer of 2; and a decoding step of, for a time period in which an input code representing a sound signal is a pair of a monaural code and an extension code corresponding to a sound signal of one point, obtaining a provisional decoded sound signal by decoding the monaural code included in the input code representing a sound signal which is the pair by a first decoding scheme corresponding to the first coding scheme, obtaining decoded difference information from the extension code included in the input code representing a sound signal which is the pair, and obtaining C decoded sound signals from the provisional decoded sound signal and the decoded difference information by regarding the provisional decoded sound signal as a mixed signal of the C decoded sound signals and regarding the decoded difference information as information corresponding to a difference between the C decoded sound signals, and outputting the C decoded sound signals, for a time period in which an input code representing a sound signal is one monaural code corresponding to a sound signal of one point, obtaining one decoded sound signal by decoding the one monaural code by the first decoding scheme and outputting the one decoded sound signal, and for a time period in which an input code representing a sound signal is k monaural codes corresponding to sound signals of k points, obtaining k decoded sound signals by decoding each of the k monaural codes by the first decoding scheme and outputting the decoded k sound signals, k being an integer of 2 or greater. a coding step of, for a predetermined time period, obtaining a monaural code by coding a mixed signal of input sound signals of C channels by a first coding scheme, obtaining an extension code including a code representing information corresponding to a difference between the input sound signals of C channels, and outputting the monaural code and the extension code as codes representing the sound signals of C channels, C being an integer of 2; and a decoding step of, for a time period in which an input code representing a sound signal is a pair of a monaural code and an extension code corresponding to a sound signal of one point, obtaining a provisional decoded sound signal by decoding the monaural code included in the input code representing a sound signal which is the pair by a first decoding scheme corresponding to the first coding scheme, obtaining decoded difference information from the extension code included in the input code representing a sound signal which is the pair, and obtaining C decoded sound signals from the provisional decoded sound signal and the decoded difference information by regarding the provisional decoded sound signal as a mixed signal of the C decoded sound signals and regarding the decoded difference information as information corresponding to a difference between the C decoded sound signals, and outputting the C decoded sound signals, for a time period in which an input code representing a sound signal is one monaural code corresponding to a sound signal of one point, obtaining one decoded sound signal by decoding the one monaural code by the first decoding scheme and outputting the one decoded sound signal, and for a time period in which an input code representing a sound signal is k monaural codes corresponding to sound signals of k points, obtaining k decoded sound signals by decoding each of the k monaural codes by the first decoding scheme and outputting the decoded k sound signals, k being an integer of 2 or greater.