To provide a method of selectively and efficiently discarding a packet stored in an FIFO buffer.

The FIFO buffer for sequentially reading data in order of writing includes a reading data designation part 109 for rewriting reading address data representing the top address of a packet to be discarded to data representing the top address of a packet next to the packet to be discarded before discarding the packet to be read next. The packet can be selectively discarded by rewriting the reading address data representing the top address of the packet to be discarded to the data representing the top address of the packet next to the packet to be discarded before discarding the packet to be read next. The packet can be efficiently discarded by only rewriting the reading address data representing the top address of the packet to be discarded.

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