In an in-vehicle image display system, each of a car navigation device and a rear-seat display device includes an own image-drawing IC. The car navigation device interfaces with a TV tuner and a DVD player. When receiving a request signal from the rear-seat display device, the car navigation device forwards relevant image data to the rear-seat display device using a dedicated line. The rear-seat display device converts the forwarded image data to image signals using the own image-drawing IC to thereby display them. Thus, the car navigation device and the rear-seat display device can display different display window images with a simple system structure where no image-drawing IC used for the rear-seat display device is provided within the car navigation device.