In an information sharing system, a data security apparatus includes a location acquisition device for acquiring GPS location information of a current location of a mobile terminal apparatus. A location evaluator checks whether the mobile terminal apparatus is located within a zone area according to the location information. A storage device stores association information of a relationship between the zone area and medical data of a medical chart allowed to be read within the zone area by authorization. A cancellation signal generator generates a cancellation signal for instructing cancellation of the medical data in case the location evaluator judges that the mobile terminal apparatus is moved out of the zone area. Furthermore, a data distributer transmits the medical data to the mobile terminal apparatus. In case the location evaluator judges that the mobile terminal apparatus has entered the zone area, the data distributer starts transmitting the medical data.