A display operating system which can freely set numbers of rows and columns in an arrangement of selection buttons displayed on a monitoring screen with immediate selection of a desired selection button being made possible. A position corresponding to that of a fingertip interrupting two of a plurality of light beams projected in a lattice on a panel of a controller at an intersection thereof is set as a first-touch position, on the basis of which an active area is established. This makes, of a plurality of selection buttons, selection buttons in the active area become selectable. Further, when the active area is changed by changing the first-touch position with a change in fingertip position to change light beams that are interrupted, selection buttons in the changed active area become selectable.