The unicycle operation is a good exercise for training of the sense of balance, the agility and the ability to coordinate the body according to situations. This paper aims to give an interpretation of the relationship between the moment balancing point (MBP) and the center of pressure (CP) in a riding a unicycle from the human motion viewpoint. This paper shows derivations of Human-Unicycle model motion equations according to the Projection Method, and represents the relationship between the MBP and the CP of the the model by considering structure and constraint reaction forces of the model.