A system for synchronizing a state of a member server with a state of other member servers belonging to a same replication group, the system including: a server sequence storage unit storing a first server sequence; a message receiving unit receiving an external message from a service server and receiving a second state update message from a second member server belonging to the same replication group including the member server, the second state update message including a second server sequence; an external message processing unit, in response to the receiving the external message, increasing the first server sequence by a predetermined value, generating a first state update message including the first server sequence, and transmitting the first state update message to the second member server; and a state update message processing unit, in response to the receiving the second state update message, changing the first server sequence to the second server sequence when the second server sequence included in the second state update message is larger than the first server sequence stored in the server sequence storage unit.