Abstract: A multichannel ADPCM compression and expansion device includes N sets of input and output interfaces; an ADPCM compression and expansion device which expansively converts data of K bits in a form of ADPCM signals into PCM signals of M bits in response to a first control signal and outputs the same and compressively converts data of M bits in a form of PCM signals into ADPCM data of K bits in response to a second control signal; and a control unit which divides one signal transmission slot interval into N sections and successively selects the N sets of input and output interfaces in a predetermined order during respective divided intervals divided into N sections and connects to the ADPCM compression and expansion device, and successively performs, while separating the divided interval into a former half and a latter half, a first control which generates the first control signal and sends the data of K bits to the ADPCM compression and expansion device and then returns the expansively converted M bit data to t