This paper discusses hand shapes for Human Computer Interface. Usually, a hand gesture based Human Computer Interface is developed by human centered design concept. A system designer or developer tends to select hand shapes by himself/herself without verifying practical effectiveness from the standpoint of system aspect. Instead, a methodology of training and recognition of hand shapes is often discussed. On the other hand, this paper listens to system's voice; which hand shape is easy to be recognized, which is easy to be confused and so on. Actually, 37 kinds of tentative hand shapes were investigated from the viewpoint of system-friendly hand shape. Based on the result, a supporting system was developed for a system designer, which helps to find appropriate hand shapes which satisfy both "user-friendly" and "system- friendly" demand.