Provided that a first segment is an earliest time segment included in a discrete time segment, and a second segment is a time segment subsequent to the first segment, a positive second-segment parameter that corresponds to a weakly monotonically increasing function value of an average amplitude of prediction residuals in a time segment including the second segment is used as a parameter for variable length coding of prediction residuals in the second segment. In addition, a value that corresponds to a weakly monotonically increasing function value of the sum of the second-segment parameter and a positive additional value that corresponds to an index representing the prediction effectiveness of time-series signals in the time segment including the second segment is used as a parameter for variable length coding of the prediction residual at a certain discrete time in the first segment.