A method of realizing uniqueness assurance includes: selecting a server to which a first message is to be transferred from multiple servers and transferring the first message to the selected server when the first message is received from a terminal apparatus by a load sharing apparatus; storing a second message that should be transferred to the same server as that of the first server when the second message is received from the terminal apparatus by the load sharing apparatus after the first message is transferred; generating uniqueness assurance information corresponding to the communication protocols corresponding to a session generated by the server to which the first message is transferred, the uniqueness assurance information indicating the correspondence between the session and the message corresponding to the session; and transferring the second message in accordance with the generated uniqueness assurance information if the stored second message exits.