In a shared-buffer-type ATM switch including a multiplexer, a shared buffer memory, a demultiplexer, a buffer memory controller, a cell copy section is disposed between the multiplexer and the memory. The copy section produces a plurality of copies of a broadcast cell according to information of a copy information table and adds associate routing information to each copied cell so as to write the cells in the memory. In response to an indication from an output counter, the cells are read from the memory to be distributed to output ports, thereby implementing a broadcast function.