Disclosed is an apparatus which, even when it becomes impossible to take an image of a mobile object due to existence of an obstacle to hide the mobile object, is capable of making a simulatory screen display of the mobile object, thereby notifying a driver of a risk of collision with the mobile object. Even when it is impossible to take an image of the mobile object because of existence of an obstacle, the apparatus displays a simulated picture image of the mobile object superimposed on an actual picture image, by obtaining an optical flow or by performing pattern matching. Thus, an effect is obtained that the mobile object is viewed as if transmitted through the obstacle. By notifying the driver of the risk of collision in advance by means of sound or video image perceptible by a human being, the danger of the collision is avoided.