To realize the round-robin retrieval at a high speed in a simple constitution which handles a plurality of priority classes fixedly or dynamically in the packet communication.

On the occasion of selecting either one (FIFO#k) of a plurality of buffers 100 FIFO#0 to #n-1 having stored communication packets 102 in the route-robin system to transmit packets stored in the (FIFO#k), the k-th buffer FIFO#k in the round-robin retrieving order about the FIFO#0 to #n-1 is enabled to send packets, a first binary variable WDR (n-1:0) with a k-th bit, as counted from the least significant bit, set to 0 and others set to 1 is generated, and the least significant bit among the bits of 0 in the first binary variable WDR (n-1:0) is specified to specify an FIFO#k to be selected from this bit position.