An action of a robot included in a robot system is controlled based on a learning result of a machine learning device. The machine learning device includes a behavior observing unit, a displaced amount observing unit, and a learning unit. The behavior observing unit observes a behavior pattern of the robot picking out a workpiece from a container. The displaced amount observing unit observes, based on pieces of image data captured before and after the pick-out action of the robot and output from an image capturing device, a workpiece displaced amount indicating a displaced amount of an untargeted workpiece in the container caused by picking out a targeted workpiece from the container. The learning unit learns an influence rate on the untargeted workpiece with an associated behavior pattern of the robot for picking out the targeted workpiece from the container, the influence rate depending on the workpiece displaced amount.