PURPOSE: To constitute the device so that numerical data can be read easily from a screen of a graphic display by displaying graphically a value of a parameter for showing an operating state by taking the axis of abscissa as time, and outputting the value of the parameter within a designated period by a numerical value in a shape of a table.

CONSTITUTION: When a display of access information of one of tables 14-1-14-5 is designated by using a keyboard of an input/output device 32 and a mouse 34, a performance information monitoring part 10 displays a prescribed screen on a display of the input/output device 32. This screen counts the number of insertion lines and the number of retrieval lines at every minute within a prescribed time, for instance, for one minute with regard to its table and displays them graphically by taking the axis of abscissa as time. By moving a ruled line 40 superposed and displayed on this screen by using the mouse 34, a position A and a position B are designated. The performance information monitoring part 10 displays the number of insertion lines, the number of retrieval lines and their total value in each time extending from the time A to the time B, as numerical values.