A switch has a determining section and a memory managing section. The determining section determines whether or not the node is in a non-ordinary state in which received packets cannot be successfully processed, on a basis of a determination whether or not congestion notification packets received from a node have been continuously received during at least a given period and a determination whether or not a quantity of memory used in a buffer memory which accumulates received packets is at least a given value. The memory managing section deletes, in a case where the node is determined to be in the non-ordinary state, data addressed to the node in the non-ordinary state among data accumulated in the buffer memory.