PURPOSE: To perform the trial/error processing with high efficiency in case a user is unable to decide previously the executing conditions and data, by displaying the original information, the command executing conditions and the result information on three different windows.

CONSTITUTION: A table serving as an original data and a command menu that can be applied to the table are first displayed on two windows as shown in a state 41. Then a single command for production of a graph, for examaple, is selected by a mouse and a table where the executing conditions for the graph producing command written is shown in a 42 state. Thus the title, type, the color, etc., are designated to said table. When a process 'tentative execution' for trial and error is selected by the mouse in the state 42, a 3rd window is produced in a state 44 for display of a completed graph. Then a window where the executing conditions are written as shown in a state 45 is moved up for re-execution after correction of conditions. Furthermore the window of a table can also be moved up for correction of data.