Provided are a display control method by which the user can cause, with enhanced ease of use, one display device to display multiple screens, and a computer program, a display control device, and an image display system. A working area generation unit generates multiple areas corresponding to multiple display areas displayed on a display screen and positions the generated areas in a working area. When only a display area A (parent screen) is displayed on the display screen (when the PinP function is disabled), a pointer position monitoring unit determines whether the pointer position has moved from an area a to an area b and outputs the determination to a simultaneous display command generation unit. If so determined, the simultaneous display command generation unit outputs a PinP function enable command to a display device.