An interface unit, which is: configured to be used for a nurse call system for forming a speech path among a plurality of slave units and a plurality of extension terminals to conduct a call, comprising a nurse call controller accommodating the plurality of slave units, and a private branch exchange accommodating the plurality of extension terminals; and provided between the nurse call controller and the private branch exchange, adapted to be connected with the nurse call controller through N number of ISDN,Integrated Services Digital Network, basic interfaces, N being a natural number between 2 and 11 inclusive,_and adapted to be connected with the private branch exchange through an ISDN primary rate interface, to interface between the ISDN primary rate interface controlling a plurality of data channels with one control channel and the N number of ISDN basic interfaces that functions as an interface controlling all of 2N data channels with one control channel, by controlling all of the 2N data channels of the N number of ISDN basic interfaces with the one control channel of the ISDN primary rate interface and the one control channel of one ISDN basic interface in the N number of ISDN basic interfaces and allocating the 2N data channels of the N number of ISDN basic interfaces on the nurse call controller side to data channels of the ISDN primary rate interface on the private branch exchange side in order from the first data channel. configured to be used for a nurse call system for forming a speech path among a plurality of slave units and a plurality of extension terminals to conduct a call, comprising a nurse call controller accommodating the plurality of slave units, and a private branch exchange accommodating the plurality of extension terminals; and a nurse call controller accommodating the plurality of slave units, and a private branch exchange accommodating the plurality of extension terminals; and provided between the nurse call controller and the private branch exchange, adapted to be connected with the nurse call controller through N number of ISDN,Integrated Services Digital Network, basic interfaces, N being a natural number between 2 and 11 inclusive,_and adapted to be connected with the private branch exchange through an ISDN primary rate interface, adapted to be connected with the nurse call controller through N number of ISDN,Integrated Services Digital Network, basic interfaces, N being a natural number between 2 and 11 inclusive,_and adapted to be connected with the private branch exchange through an ISDN primary rate interface, to interface between the ISDN primary rate interface controlling a plurality of data channels with one control channel and the N number of ISDN basic interfaces that functions as an interface controlling all of 2N data channels with one control channel, by controlling all of the 2N data channels of the N number of ISDN basic interfaces with the one control channel of the ISDN primary rate interface and the one control channel of one ISDN basic interface in the N number of ISDN basic interfaces and allocating the 2N data channels of the N number of ISDN basic interfaces on the nurse call controller side to data channels of the ISDN primary rate interface on the private branch exchange side in order from the first data channel. by controlling all of the 2N data channels of the N number of ISDN basic interfaces with the one control channel of the ISDN primary rate interface and the one control channel of one ISDN basic interface in the N number of ISDN basic interfaces and allocating the 2N data channels of the N number of ISDN basic interfaces on the nurse call controller side to data channels of the ISDN primary rate interface on the private branch exchange side in order from the first data channel.