Abstract: A method of generating association rules from a data stream, which is a non-limited data set composed of transactions, includes: when itemsets in the generated transactions and the counts of the itemsets are managed using a prefix tree, and each node of the prefix tree has information on the count of a specific itemset corresponding to the node and a specific item, updating the information of a node corresponding to the itemset or adding a new node on the basis of the itemset included in the generated transaction and the count of the itemset; comparing the support of the itemset corresponding to each of the nodes of the prefix tree with a minimum support to select frequent itemsets; and visiting all or some of the nodes corresponding to the selected frequent itemsets and generating the association rule on the basis of the information of each of the visited nodes.