To enable to perform operation and display easily at a standing position or sitting position by attaching a foot operator provided with a foot operated pointing device cooperating with a computer display device and an execution means for selected screen modes.

Several menu screens are set according to various examination data of a patient, details of the examination data, etc., in advance. An operator put his foot on a pedal 5 of a foot operator 17, seeks an intersection point of the pointing device by moving the pedal 5 up and down/right and left, and selects the position of a displayed image. That is, an X axis is selected by moving the pedal 5 right and left. A Y axis is selected by moving the pedal 5 up and down. When the pedal 5 is moved in a right and left direction 10, light is output from a light projector 22 at the back of the pedal 5. When moved in the up and down direction 9, light is output from a light projector 25. These lights are inputted to a processing computer through a right and left light receiver 23 and an up and down light receiver 24, and the screen is controlled.