An example game system includes a home-console type game device, a controller device, and a portable display device. The portable display device includes an infrared emitter capable of emitting infrared light. The controller device wirelessly transmits to the game device operation image data from an image-capturing section, inertia sensor data, and operation button data. The game device receives the operation data from the controller device, and performs game processes based on the operation data. Moreover, the game device compresses first game images, which are generated based on the game processes, to generate compressed image data. The compressed image data is wirelessly transmitted to the portable display device. The portable display device receives the compressed image data from the game device, expands the compressed image data to obtain the game images, and displays the game images.