In a through type motor having a ball screw shaft (24) penetrating therethrough and driving it for rotation, flow paths (28, 30, 32) for passing compressed air for cooling are provided on one of the sides of the motor which is closer to a ball nut (22) lest the generated heat of the motor is transferred to the ball screw shaft (24) through the ball nut (22) that is fitted to one of the ends of a cylindrical shaft (20) of the through type motor and meshes with the ball screw shaft.
