A CAD apparatus configured to display and edit graphic data including a layer that includes a circuit diagram that is basic to a drawing of an electric system, and one of a layer that includes comments about the circuit diagram, a layer that includes restrictions for designing the circuit diagram, a layer that includes a result of Design Rule Check, a layer that includes an analysis result obtained by a simulator, a layer that includes information about specifications of parts of the circuit represented by the circuit diagram, the CAD apparatus comprising: - a layer-information storage unit that stores a layer management table (141 a) that manages an order of said layers and display flags and edit flags of each of said layers, and page lists that manage information about pages included in each layer; - an element-information storage unit; - an association-information storage unit; - a layer displaying unit that displays elements stored in an element list of said element-information storing unit and comprising symbols of parts arranged on the circuit diagram and wiring that connects the parts, and character information and storing an identification number, a next pointer, an association pointer, a page pointer, and an origin pointer, which are common to all elements, in addition to information unique to the element, which is graphic information and character information, the next pointer being a pointer that indicates the next member in the element list, the association pointer being a pointer that indicates an association list stored in the association-information storage unit and for associating an element of the layer that includes a circuit diagram with at least one element of another layer among the layers, and the page pointer being a pointer that indicates a page object connected to the element list in which the element is included, the origin pointer being a pointer that indicates an original element, if the element is an element created by graphic element conversion, said elements being included in each of said layers that form the graphic data onto a display unit in a superposed manner. - a layer-information storage unit that stores a layer management table (141 a) that manages an order of said layers and display flags and edit flags of each of said layers, and page lists that manage information about pages included in each layer; - an element-information storage unit; - an association-information storage unit; - a layer displaying unit that displays elements stored in an element list of said element-information storing unit and comprising symbols of parts arranged on the circuit diagram and wiring that connects the parts, and character information and storing an identification number, a next pointer, an association pointer, a page pointer, and an origin pointer, which are common to all elements, in addition to information unique to the element, which is graphic information and character information, the next pointer being a pointer that indicates the next member in the element list, the association pointer being a pointer that indicates an association list stored in the association-information storage unit and for associating an element of the layer that includes a circuit diagram with at least one element of another layer among the layers, and the page pointer being a pointer that indicates a page object connected to the element list in which the element is included, the origin pointer being a pointer that indicates an original element, if the element is an element created by graphic element conversion, said elements being included in each of said layers that form the graphic data onto a display unit in a superposed manner.