When a switching unit of each of first DB servers receives a transaction-stop instruction request from a second DB server, the switching unit performs a transaction-stop instruction process. When a transaction processing unit of each of the first DB servers receives a transaction stop instruction from the switching unit, the transaction processing unit performs a transaction stop process. In the same manner, a transaction processing unit of the second DB server performs a transaction stop process. Each of the transaction processing units of the first and second DB servers determines whether a transaction is to be stopped depending on a processing attribute and a processing state of an SQL included in the transaction and then performs the transaction stop process depending on a determination result of the processing attribute and the processing state.