A robot system includes two arms, each having a hand at an end thereof, and a controller to control operation of the arms. The hand has an openable and closable holder. The controller includes hand-number determining circuitry to determine the number of hands used to hold a holdable object based on the size of the holdable object, and hold controlling circuitry to control the holder of one of the hands to open so as to hold the holdable object by an inner surface of the holder, when the number of hands to be used is one, and control the holders of the two hands to close so as to hold the holdable object by outer surfaces of the two holders, when the number of hands to be used is two.