To perform high-speed and easy round robin retrieval whether fixedly or dynamically and to perform the high-speed and easy round robin retrieval handling a plurality of priority classes.

A round robin unit 400 is provided in each of a plurality of areas of a cell buffer 203 and connected through a loop-shaped retrieval route. Each unit is provided with a register part 601 for holding information regarding cells stored in the area of the cell buffer, and a retrieval part 602 and an output control part 603 for outputting a retrieved result for selecting one of a plurality of the cells stored in the cell buffer from the final stage by generating logic signals corresponding to a logic state of holding information of the register part and the logic state of the retrieved result of a preceding stage and shifting them to the post stage by circulating a retrieval pointer on the loop-shaped retrieval route.