A session management system including a client environment providing server including at least one client environment (41-n) including a message processing unit (43-n), a plurality of terminals, and a session management server which manages a session between said client environment (41-n) and said terminals, wherein said session management server comprising: a session monitoring unit which monitors use end time of said client environment (41-n); a client environment management unit which makes a log-out request for the execution of log-out processing of a predetermined client environment (41-n) to said client environment providing server; and a state of use checking unit which checks a state of use of each said client environment (41-n); a storage device which stores a connection destination setting table which stores a usable client environment (41-n), use start time, use end time and extendable time so as to be correlated with each other on a user basis, wherein said session monitoring unit refers to said connection destination setting table and compares the current time and the use end time of said client environment (41-n) to notify to said state of use checking unit a request for transmitting a warning message display request which makes said client environment (41-n) display a warning message that urges logout when the use end time of said client environment (41-n) is within a fixed time range from the current time, said state of use checking unit checks a state of use of said client environment (41-n), said client environment management unit, when said client environment (41-n) is in use, transmits said warning message display request to said client environment providing server, said client environment management unit transmits said warning message display request with said extendable time included to said client environment providing server when said extendable time is set, said message processing unit (43-n) inquires of said user whether use time is to be extended when said warning message display request includes said extendable time, said message processing unit (43-n) transmits an extension notification to said management server when said user selects extension, said client environment management unit extends corresponding use end time based on said extension notification, and updates use start time overlapping with the extended use end time to the extended use end time, said session monitoring unit notifying a request for stopping use of said client environment (41-n) to said state of use checking unit when the use end time of said client environment (41-n) coincides with current time, and said client environment management unit, when said client environment (41-n) is in use, transmitting to said client environment providing server a log-out request for the execution of the log-out processing of said client environment (41-n). a session monitoring unit which monitors use end time of said client environment (41-n); a client environment management unit which makes a log-out request for the execution of log-out processing of a predetermined client environment (41-n) to said client environment providing server; and a state of use checking unit which checks a state of use of each said client environment (41-n); a storage device which stores a connection destination setting table which stores a usable client environment (41-n), use start time, use end time and extendable time so as to be correlated with each other on a user basis, wherein said session monitoring unit refers to said connection destination setting table and compares the current time and the use end time of said client environment (41-n) to notify to said state of use checking unit a request for transmitting a warning message display request which makes said client environment (41-n) display a warning message that urges logout when the use end time of said client environment (41-n) is within a fixed time range from the current time, said state of use checking unit checks a state of use of said client environment (41-n), said client environment management unit, when said client environment (41-n) is in use, transmits said warning message display request to said client environment providing server, said client environment management unit transmits said warning message display request with said extendable time included to said client environment providing server when said extendable time is set, said message processing unit (43-n) inquires of said user whether use time is to be extended when said warning message display request includes said extendable time, said message processing unit (43-n) transmits an extension notification to said management server when said user selects extension, said client environment management unit extends corresponding use end time based on said extension notification, and updates use start time overlapping with the extended use end time to the extended use end time, said session monitoring unit notifying a request for stopping use of said client environment (41-n) to said state of use checking unit when the use end time of said client environment (41-n) coincides with current time, and said client environment management unit, when said client environment (41-n) is in use, transmitting to said client environment providing server a log-out request for the execution of the log-out processing of said client environment (41-n).