A communication system (1) comprises a central (100) and a peripheral (200). The central (100) receives location information and time information from NTP servers (10) and a location server (30). The central (100) creates first offset information of the time measured by its own device and the time information received from the NTP servers (10). The central (100) acquires from map information a time difference corresponding to a location presented by the location information received from the location server (30). The central (100) creates first updated time information based on the time measured by its own device, first offset information, and time difference corresponding to the location presented by the location information received from location server (30) and transmits the first updated time information to the peripheral (200). The peripheral (200) changes the time displayed by its own device based on the received first updated time information.