In a drive apparatus for a toggle-type mold clamping mechanism of a vertical injection molding machine, a drive motor movably supported on a guide table via rollers moves horizontally following the vertical movement of a ball screw, when a mold is opened or closed, with keeping the distance between the ball screw and the output shaft of the drive motor constant by means of connecting plates. As the ball screw is rotated by the drive motor via a first pulley, a second pulley and a belt wound around the first and second pulleys, a toggle arm of each of a pair of symmetrical toggle clamping mechanisms is bent to close or open the mold.