PURPOSE: To prevent switching in the middle of transaction at the time of switching a terminal connected with a distributed computer to the other distributed computer, in an on-line transaction processing system.

CONSTITUTION: When a switching control part 22 receives the instruction of terminal switching from a distributed computer 3 to a distributed computer 4 from an inputting device 1, it instructs a line control part 32 to close a terminal 6, and simultaneously instruction a line control part 42 to open the terminal 6. The line control part 32 receives the close instruction, refers to a transaction information table 33, and set a flag indicating that the close instruction is being accepted at a line control table 34 when the terminal 6 is in the meddle of the transaction. When the transmission of a response from a transaction response control part 21 to the terminal 6 ends, a transaction control part 31 refers to the flag of the line control table 34, and issues the close request of the terminal 6 to the line control part 32. The switching control part 22 receives close and from the line control part 32, and instructs a line switching device 5 of line switching, and the switching is ended.