An object is to provide a traffic monitoring method, a traffic monitoring apparatus, and a program capable of efficiently merging data structures of each of the cores in a multi-core environment without reconstructing a data structure, retrieving a data structure, and adjusting the RSS function. In the traffic monitoring method according to an embodiment of the present invention, the elements of the data structures formed in the cores are compared for each item, and statistic values in the elements are brought together into any one of the elements, and the statistic values of the other elements are set to zero. Redundant elements between the data structures can be removed by ignoring elements having a statistic value of zero at the time of merging data structures.