In a design-system distributing method, when a server side design system is updated, a server compares an updated server side design system and a client update state data, and the server distributes an update assisting system, an update indication data and a difference data to a client system based on the comparing result. The client system stores the update assisting system, the update indication data and the difference data, and the client system starts the stored update assisting system such that an update notice is outputted to a user of the client system to urge update of the client side design system each time a preset condition is satisfied until an update command of the client side design system is supplied to the client system. The client system updates the client side design system based on the stored update indication data and the stored difference data in response to the update command. The client system generates and transmits the client update state data to the server to indicate an update state of the client side design system for this time, and the server updates the client update state data based on the client update state data received from the client system.