We have developed a fast target tracking system that utilizes four cameras with lenses of different focal lengths to track an object without blurring images, even when the object moves in the depth direction away from the cameras in three-dimensional (3-D) space. This system can maintain a well-focused camera view by switching among the four input images, instead of using lens motor control. The multi-camera system was mounted on a two-axis mechanical active vision platform. The active vision control and camera-view switching are executed by processing color 512 × 512 images from the four camera inputs at 500 fps in real time on a high-speed vision platform. The performance of our system was verified by its tracking results for objects moving rapidly in 3-D space.