Abstract: An improved time slot allocation method for a loop network. Loop networks in which the present invention is applied include a loop-connecting a control station and a number of branch stations. The control and branch stations each have at least one terminal connected thereto such that interstation communication, when demanded by a terminal, is made by passing a frame through the transmission path. The frame includes a synchronization area for indicating the leading end of the frame, a fixed-length control area, and a data area composed of a plurality of time slots. According to the invention, the control and branch stations are each allocated with a predetermined or unique number of time slots to be used by terminals for interstation communication. When a station has its reserve of unused time slots fall below a preset lower limit, the control station supplements time slots from its own reserve.