Between digital data signals, which are expressed using a notation system of three digit symmetric binary numbers (named “HEN2”), and analog signals, at least one way, mutual, or other conversions are made. Three digit symmetric binary numbers (HEN2), are a combination of signals in which at least one of two adjacent digits, at any digit position of one or more digits of 2-based three digit redundant binary numbers with one signal of three digits {n, o, p} expressing a value {−1, 0, 1} as a one-digit signal, is a signal “o” expressing zero. Thus three digits {−1, 0, 1} are used instead of the two digit {0, 1} binary system used in conventional A/D or D/A converters.