PURPOSE: To prevent misoperation by an operator of a switchboard by digitizing entirely an interface between a switchboard and a high-order system and incorporating a tone section to the operator of switchboard so as to reduce the number of interface lines to the high-order system.

CONSTITUTION: A digital switchboard 10 and a high-order system 20 are connected by a data line 11, and the information with a system 20 is received and transmitted by a transmission and receiving section 1 of the device 10. Further, a separating section 2 separates the information from the system 20 into a voice data 14 and a control data 15, applied to a converting section 3 converting the data 14 into an analog quantity and the data 15 is applied to a connecting section 5 connected to a tone setcion 4. Moreover, a speech data from a converting section 3 and a control data from a control section 5 are inserted to time slot corresponding respectively inversely from a branching section 2. Further, a man-machine device 6 is connected to the control section 5, the interface between the device 10 and the system 20 is all digitized, the number of data lines 11 is reduced and the misoperation of the operator of switchboard is prevented.