A method for providing design data and a system for providing design data that enable a lens processor to manufacture a desired inner-surface progressive addition lens corresponding to prescription data. A design data providing system is a system such that a design data creator provides design data of an inner-surface progressive addition lens to a lens processor in the case where the lens processor has agreed upon a contract to the effect that the lens processor receives provision of the design data of the inner-surface progressive addition lens from the design data creator on the condition that the lens processor pays a consideration. The design data providing system has a server device as a host computer device, a terminal computer device, and a network for connecting the server device to the terminal computer device.