To provide a differentially encoded signal decoding device capable of compensating a section, if any, where no encoded signal arrives without producing an abnormal sound nor processing delay.

The differentially encoded signal decoding device decoding an input encoded string subjected to differential encoding has: a pseudo-code generator which generates a pseudo encoded string to be decoded instead of the input encoded string, a switch which selects the input encoded string or pseudo encoded string, a decoder which decodes the encoded string selected by the switch, and a signal synthesizer which selects and outputs a decoding result of the decoder or an internally generated alternative signal according to whether the input encoded string can be used.