A contactless data communication system includes a contactless identification tag having first identification information inherent to the contactless identification tag and includes a drive power generation means to generate drive power from an electromagnetic wave used for a power supply sent from a data communication system, an acquisition request receiving means, and an identification information sending means. The contactless data communication has a second identification information inherent to the data communication system and includes an electromagnetic wave sending means, an identification information acquisition means, an information sending means, an information acquisition means, and a position information computation means.