In order to calculate a ball screw abrasion amount of an injection-axis ball screw or a mold-clamping-axis ball screw, a position of a ball nut fitted to the ball screw is photographed by a camera installed in an injection molding machine. Then, if the photographed position of the ball nut is found, as a result of analysis of an image captured by the camera, to be deviated from the position of the ball nut when a ball screw has no abrasion, it is determined that the ball screw is abraded.

A mold clamping device includes two mold platens; a plurality of ball screw mechanisms connecting the mold platens to each other; and a plurality of servo motors configured to drive the respective ball screw mechanisms. Each of ball screws respectively configuring the plurality of ball screw mechanisms is provided with a cover which covers at least a part of the corresponding ball screw between the two mold platens.