Abstract: Provided is a design assistance system that enables a user having no expert knowledge to easily design a network system, taking into consideration the order in which slave devices are connected and the connection-destination ports. The design assistance system has a storage section that stores slave information data in which unique information of the slave device is described; an acquisition section that acquires information of a port of the slave device from the slave information data; and a generation section that generates a port component serving as a GUI component representing the port of the slave device based on the information of the port, generate a device component serving as a GUI component representing the slave device based on the slave information data, and generate a design assisting GUI containing a topology display screen that displays the topology of the network system which includes the device component and port component.