This disclosure discloses a robot hand of underactuated mechanism. The robot hand includes a plurality of actuators, a plurality of joints where the number of the joints is more than the number of the actuators, a palm portion, three finger portions each including a plurality of links having bases coupled to the palm portion and coupled being capable of flexion, and a shape-fitting mechanism which is provided in at the finger portion, and which enables to grasp an object to be grasped in an enclosing manner with the finger portions by performing providing torsional displacement to the links.