Considering the locations of a self-vehicle and other vehicles changing from moment to moment, an image signal is chosen in relation to the location, orientation, viewing angle, and moving speed of a camera mounted on each vehicle, and information on a region to be a driver's blind spot is provided in real time by means of images and voice. When there is the other vehicles whose camera meets requirements such as the location, orientation, viewing angle, and moving speed for photographing a region to be the self-vehicle's blind spot, it is possible to provide information on the blind spot by the image picked up by the camera. However, since the other vehicle's location also changes with a lapse of time, it is not possible to keep photographing the blind spot with the same camera. Therefore, the image of the driver's blind spot is obtained in real time by constantly detecting the location, orientation, viewing angle, and moving speed of cameras mounted on the other vehicles running near the self-vehicle, choosing dynamically a camera capable of photographing the region to be the self-vehicle's blind spot, and switching image signals in succession.