PURPOSE: To minimize the time delay by performing the exchange processing and the repeating processing based on the cell phase detected by a received cell flow.

CONSTITUTION: A phase detection circuit 3 receives the cell flow passing a transmission line 21 and outputs the received cell flow 3B to a cell processing circuit 5 and detects a cell phase 3A indicating the cell boundary from the received cell flow and outputs the detected cell phase 3A to a phase supply circuit 4. This circuit 4 generates timing signals 4A, 4B, and 4C based on the cell. phase 3A outputted from the phase detection circuit 3. The cell processing circuit 5 receives the cell flow 3B outputted from the phase detection circuit 3 and executes the exchange processing and the repeating processing of the cell flow based on timing signals 4A, 4B, and 4C generated in the phase supply circuit 4.