1. A communication control apparatus, comprising: a storage device for storing search information to determine a subsequent transfer route for a packet received by way of its destination address; and a route search device to search for a transfer route for said packet received based on said search information, wherein said search information is associated with a tree structure, each node in said tree structure having at least one entry, a mask prefix associated with said at least one entry, wherein each entry includes information on the number of bits of said mask prefix associated therewith, and a sort key, and wherein the number of bits of said sort key is set to be greater than or equal to the longest mask length amongst the mask lengths of all said mask prefixes; a bit string divided into an upper side bit string field and a lower side bit string field, wherein the upper side bit string field of each of said sort keys is to match said mask prefix associated with an entry having said sort key wherein entries are assigned to predetermined nodes of said tree structure based on the sort order of their sort keys; each node having an entry list in which multiple entries included therein are sorted based on their sort keys; and each node except leaf nodes are linked via each branch to relate each entry in the entry list of said node to each node at the next lower hierarchy.