Time division multiplex transferring system capable of increasing transferring efficiency and preventing interruption of communication

In a time division multiplex transferring system which uses fixed setting, on-demand, and frame relay bandwidths, a first time switch allocates the on-demand and frame relay bandwidths in response to a first allocation setting datum to produce two output signals. A second time switch allocates the on-demand and frame relay bandwidths in response to a second allocation setting datum to produce two output signals. A bandwidth allocation controlling device produces and renews the first and second allocation setting data in response to the connectivity restriction to produce and transmit a first allocation change datum to a counter node. The bandwidth allocation controlling device thereafter produces a first allocation end signal in response to a second allocation end signal from the counter node. The bandwidth allocation controlling device renews the first and second allocation setting data in response to a second allocation change datum from the counter node and thereafter produces and supplies the first allocation end signal to the counter node. A bandwidth switch controlling device produces a first switch signal in response to the first allocation end signal and produces a second switch signal in response to a second switch bit. A selector selects and transmits one of the output signals of the time switches in response to the first and second switch signals, respectively.