A service providing system for improving convenience of users by quickly executing a membership registration process in a system in which plural shops and groups jointly administrate its members. In the system, an external reading/writing unit stores a write data table in which provider-side data is correlated with information notification level, a portable information terminal enables the user to select the information notification level in accordance to a control of a portable terminal-side application and writes user-side data correlated with the information notification level selected by the user in the notification data table and the information notification level selected by the user to a non-contact IC. The external reading/writing unit reads the user-side data and the information notification level out of the non-contact IC, stores the user-side data and writes the provider-side data correlated with the information notification level in the write data table to the non-contact IC.