Packet transfer device and method have both a processing procedure for uninterruptible-switching desiring packets and a processing procedure for low-delay desiring packets, and process each user packet according to a desired one of the processing procedures. The uninterruptible-switching desiring packets are set to be in phase by a delay unit and written into an uninterruptible-switching memory. The low-delay desiring packets are written into a low-delay memory without passing trough the delay unit, that is, without being delayed. A read-out controller reads out a packet from the uninterruptible-switching memory. When the read-out packet is an uninterruptible-switching desiring packet, the packet is directly output, and when the read-out packet is a low-delay desiring packet, the packet is discarded, and a low-delay desiring packet is read out from the low-delay memory and output.