In regard with the precision positioning devices using the ball screw, its temperature rises during operation and this causes positioning error. In this paper, a ball screw temperature is decreased by cooling the nut from outside using two kinds of water jackets. This method is effective and very cheap. In case of the first jacket (D type), the water circulates along the double spiral grooves while in case of the second jacket (G type), cooling water moves going and returning inside the flow path along the longitudinal direction and the water circulates in the holes. By these two kind of jackets, the nut is cooled and at the same time the ball screw is cooled indirectly. The temperature of the ball screw and nut are measured by surface temperature measuring instrument and thermocouples. As a result, the followings are clarified. (1) D type is more effective than G type. (2) The ball screw temperature can be estimated by measuring the nut surface temperature.