We developed a novel robot hand using an iris mechanism similar to that used as a lens aperture in cameras. An iris mechanism is useful because it opened and closed from all directions, but has not been considered practical for use as a robot hand because the iris blades are thin and overlap one another. In this research, we developed a structure using thick blades that do not overlap, thereby allowing it to be use as a robot hand. The resulting mechanism is driven by a single actuator. Because objects can be grasped from all directions, iris robot hands can grasp any object placed in the hand opening. We developed two types of iris robot hands: a sliding type driven by a slider and a swinging type driven by gear rotations. We then analyze the developed iris robot hand to verify its characteristics and effectiveness.