A searching method for tree data structure topology employs an array generated as a search key array representing a tree serving as search key to represent a parent-child relationship between nodes. The array has the node identifier assigned to a parent node associated with a corresponding non-root node. Non-root nodes are nodes other than a root node, and the node identifier assigned to the parent node corresponds to the node identifier assigned to associated non-root nodes. An offset is applied to node identifiers in the search key array, the node identifiers to which offset is applied are compared with corresponding node identifiers contained in a portion in a C-P array, the portion determined according to the offset, and a vertex node list indicating a search result is stored, wherein the search result contains node identifiers included in a portion of the C-P array whose all nodes matched in comparison.