To make comfort noise perceived comfortably by changing its energy and characteristics.

A noise parameter generator 40 which uses the average value of input signals generated in the noise analysis phase and weighted with their self-correlation values is installed. In this case, the weighting function imparts small weights on the first two or three frames(including voice in some occasions) and greater weights on the frames toward the end of this phase. To overcome the noisy nature of comfort noise, a comfort noise generator 50 which gradually varies the nature of signals after vocal burst from voice to pseudo random noise is installed. This generator 50 excites the autoregressive filter corresponding to the noise model by the weighted combination of past excitation and pseudo random noise.