In a robot hand according to the present invention, a first-type grasping claw driven by a servo motor on a hand base and a second-type grasping claw having no actuator are used with the grasping claws mounted on each holding unit. The second-type grasping claw is movable in a direction perpendicular to a moving direction of the first-type grasping claw. The robot is operated so that an external force is applied to the grasping claw by bringing the grasping claw into contact with a contact surface of a stationary stand member, thereby to change a position of the grasping claw relative to the hand base and that grasping claw is locked at that position by a brake mechanism. Each grasping claw is adapted to be able to be mounted or dismounted on or from the holding unit using a pull bolt and a retaining mechanism, and can be automatically changed by the robot operation. By attaching the pull bolt to the workpiece in advance, the retaining mechanism also can be used for holding the workpiece.