Disclosed are an opened network connection control method, an opened network connection control system, a connection control unit and a recording medium, which allow only terminal units capable of securing security to be connected to an opened network, thereby improving the security level. The connection control unit acquires connection history information held by the terminal unit which has sent a request for connection to the opened network to a central unit, and assigns a logic identifier to the terminal unit and connects the terminal unit to the opened network when the contents of the acquired connection history information coincide with the contents of connection condition information record.