Ms stereo digital audio coder and decoder with bit assortment

The MS stereo digital audio coding and decoding device for coding and decoding digital audio signal by adaptively allotting a bit to each channel comprises a middle side matrix unit for generating an audio signal of a middle channel and an audio signal of a side channel; a mutual similarity calculating unit for calculating a mutual similarity value of the audio signals for first and second channels and generating a predetermined interval of index information corresponding to the value; a coder for coding the audio signals for the M channel and S channel into the bit corresponding to the index information; an adaptive bit allocation unit for supplying a predetermined bit allocation information to the coder in response to the index information; and a multiplexing unit for multiplexing the coded audio signals for the M and S channels and the bit allocation information to generate a bit stream adequate to the channel characteristic.