To solve the problem that it is difficult to operate re-connection in an application level in a state that a session is held in operating re-connection after restoration when a communication line connecting a host computer 1 to a terminal 3 is disconnected.

In connecting a terminal 3 to a host computer 1 for the first time, the connection of the terminal 3 to a communication server 2 is operated, and session information is transmitted to the communication server 2. The communication server 2 receives the session information transmitted by the terminal 3, and operates the assignment of a terminal identifier which is not overlapped with the other terminal, and transmits the terminal identifier to the terminal 3. Afterwards, the communication server stores the session information, and operates the connection to the host computer 1. Thus, it is possible to specify the terminal to be treated as re-connection, and even when the terminal is treated as re-connection, the terminal is treated as new connection when viewed from the host computer 1. Therefore, it is possible to realize connection without generating the rejection of connection due to double log-in.