A robot system includes a three-dimensional measuring device for obtaining positional information of a workpiece, a robot having a tool capable of holding a workpiece, and a control device for controlling the robot. The control device stores association data which associate the positional information of the workpiece with a center-of-gravity position of the workpiece. A center-of-gravity position of the workpiece to be picked out is estimated, based on the positional information obtained by the three-dimensional measuring device and on to the association data. The control device determines at least one of the holding position of the workpiece, the picking-out direction and the position and posture of the tool, based on the estimated center-of-gravity position.