A data transfer system including an exchange, wherein the exchange transfers data by sharing a plurality of channels by a time division multiplex mode. In this case, the exchange transfers the data by variably allocating respective time slots to be occupied by the respective channels. That is, it is possible to allot any line speed to any channel and therefore possible to mix signals with different data transfer speeds in the frames. This results in an exchange network with a high degree of freedom of transfer for the subscriber terminal equipment.