A robot system capable of purposely withdrawing a workpiece into a hand, and capable of sequentially and effectively taking out the workpiece, even when workpieces are randomly located. A hand has a base part attached to the front end of a robot arm, at least two fingers pivotally attached to base part, and a roller device arranged at a front end of each finger. The roller device is a rotating belt device having a small motor arranged in the finger, a driving roller driven by the motor via a drive transmitting means, and a driven roller rotated with the driving roller via a belt.