PURPOSE: To provide a simultaneous generation control system to be applied to a distribution type system for processing the simultaneous generation of a transaction and an inquiry. CONSTITUTION: The consistent 'stable state' of a data base is applied to a read-only inquiry during the active period of inquiries 16, 18. An updating transaction required to be locked can be advanced without waiting the end of an inquiry for a long time. Although long time read-only inquiry to be phased out due to timeup is allowed to two or more versions without forcing a new inquiry and executing roll-back because old 'stable state' data are used, at least two data base versions are required. Since the updating of a 'stable state' data base version is allowed before the normal end of the read-only inquiry, the inquiry can be converted into a locking transaction after the end of the inquiry.