The efficiency of an AGM algorithm is further improved. For an AGM algorithm that can efficiently extract, from a graph database including graph structured data, graph (frequent graph) data having a support level equal to or greater than the minimum support level, a function "relabel" for ordering the vertex labels and edge labels of the graph is executed (step 1). Further, for a function "Newjoin", for employing a set Fk of adjacency matrixes that represent a size k frequent graph, for generating a set C_k+1 of adjacency matrixes, which represent a size k+1 candidate frequent graph, a fourth condition for coupling a first generator matrix to a second generator matrix is added to the three conditions of the AGM algorithm only when the first generator matrix is a canonical form.