PURPOSE: To display the directed graph satisfying the display requirements based on the rules for the inputted data of the directed graph.

CONSTITUTION: The connection information, etc., is extracted from the data of the directed graph inputted from a directed graph input means 11 by a logical information extraction means 12. While, the display requirements to be satisfied by the directed graph to be displayed are stored in a graph display rule storage means 13. In a calculating formal drawing means 14, the calculating formula to calculate the display position for the node of the directed graph is drawn from the rules and the extracted logic information. In a coordinate calculation means 15, the display position for each node is determined by determining the solution by adopting the calculating formula drawn by the calculating formula drawing means as an algebraic expression. When the calculating formula is not enough for deciding the the coordinate for each node at this time, the coordinate calculation means adds the calculating formula so that the calculating result can be fixed uniquely and determines the display position for each node by solving the obtained calculating formula. The result is displayed by a graph display means 16.