This paper proposes a storage structure for graph-oriented databases called the flattened separable directory method. In this method, a data representing graph, which is a unit of representing graph, is primarily represented with an array of edge or node types. As every node or edge can be accessed without navigation, the values of nodes and/or edges can be quickly evaluated. Experimental evaluations support this characteristics, and clarify that the performance of inserting data is high, and less storage overhead is needed in the case of the graphs consisting of many node and edge types.