A robot system for successively taking out bulk stacked workpieces of the same type, wherein a hand of a robot comprises: a base part attached to an arm, a cylinder device with a cylinder and a piston rod, and a gripping part attached to a front end part of the piston rod. The robot system further comprises a fluid pressure adjusting device which adjust a fluid pressure inside of the cylinder, a movement detecting device which detects a retracting movement of the piston rod, and a judgment device which judge if the hand is gripping a designated number of workpieces, based on a magnitude of fluid pressure inside the cylinder and detection results of the movement detecting device.