1. An auto-focus adjustment device comprising: a focus detecting section that repeatedly detects a focus state of a photo lens; a moving velocity determining section that determines at least a first velocity and a second velocity related to the movement of an object based on the focus states detected by said focus detecting section; an acceleration determining section that determines an acceleration of the object based on the first velocity and second velocity determined by said moving velocity determining section; a velocity ratio determining device that determines a velocity ratio for the object based on the determined velocities from said moving velocity determining section; and a forecast section that forecasts a position of the object based on the determined velocities, the velocity ratio, and the acceleration.