In a computer aided design (CAD) apparatus, an association-data acquiring unit acquires association data that defines an association between pins of a first connector and those of a second connector to be connected to the first connector, and an assignment of signals to the pins. A part-information acquiring unit acquires information including a symbol of the first connector. A layout-condition acquiring unit acquires a layout condition to lay out the symbol of the first connector on a circuit diagram. A circuit diagram creating/updating unit lays out the symbol of the first connector on the circuit diagram based on the layout condition, and adds a net name indicating a signal assigned to each of the pins to the symbol.