It is difficult to generate the action of stably pinching paper or needle, etc. with the fingertips, which is one of the important functions to be realized by humanoid robot hands In this paper, the authors propose a new robot hand capable of properly realizing a pinching motion with fingertips, by adding the minimum required degree of supplementary freedom which can be realized only with a machine. Through this designing of the mechanism, even the motion of writing characters with a pen was accomplished in our robot hand.