An auto-focusing device for stably drive a photographing lens to track a moving object comprises charge accumulation type photo-electric conversion means for accumulating charges at a predetermined time interval to produce a focus detection signal, defocus amount calculation means for calculating a defocus amount of the photographing lens based on the focus detection signal, drive distance calculation means for calculating a direction and a distance of the lens drive for driving the photographing lens to track the moving object based on at least the defocus amount, drive means for driving the photographing lens in accordance with the calculated direction and distance of the lens drive, and control means for supplying the direction and distance of the lens drive calculated by the drive distance calculation means to the drive means after the end of the next charge accumulation by the photo-electric conversion means to drive the photographing lens so that the photographing lens tracks the moving object.