To provide a multi-drop connecting method for multiframe interface improved in the availability of PBX, and to provide the interface device therefor.

At the time of mutually connecting plural stations 61, 62 and 63 connected with PBX 64, 65 and 66 through a transmission path 67 to send a multiframe from the PBX between the respective stations, the header and data of the multiframe from the PBX are decomposed into the headers and data of individual channels to form a rotation frame consisting of plural time slots housing a pair of the header and data of one channel in one time slot, this rotation frame is sent to the transmission path 67 and the respective stations 61, 62 and 63 are multi-drop-connected to this path 67.