PURPOSE: To execute an exclusive control of a file without causing the deterioration of the maintainability of data and the system performance, by providing a lock designating means for designating a lock by a key value with respect to an open file.

CONSTITUTION: A lock designating means for designating a lock by a key value with respect to an open file is provided. Subsequently, among records for constituting the file designated by this lock designating means, all of records having a key value designated by the lock designating means are locked. Accordingly, by designating one key value, many unspecific records can be locked simultaneously. In such a way, an exclusive control of the file at the time when it is attended with a set operation and a processing of plural records can be executed without causing the deterioration of the maintainability of data and the system performance, by designating a key value which becomes its object.