A low for the safety of bicycles that are able to be ridden with two children is established in 2009.Consequently, development of such bicycles has been attracting a lot of attention. To improve for the operability, we proposed a power steering system for such bicycles. But, in this case, weight and inertia of the handle is increased, and the handling is worse. In this paper, we consider the safe manual control for the bicycle. The limitation of the stability of the bicycle system is shown by the normalized dynamics.