Abstract: There is provided a method of performing priority control for cells in an output buffer type ATM switch including a switching unit, having a plurality of input ports and a plurality of output ports, for switching/outputting the cells input from the input ports to the output ports in accordance with routing information, and a plurality of output buffer units having output buffer memories, connected to the output ports of the switching unit, for temporarily storing the cells output from the output ports to perform output control of the cells. A loss quality class, a delay quality class and the routing information are added to each of the cells. A plurality of logical queues for temporarily storing the cells are virtually set in an input buffer memory in accordance with the delay quality classes and the routing information. The input cells are selectively written in the logical queues on the basis of the loss quality classes and the routing information added to the cells.