The two kinds of bicycles of the power transmission types are derailleur type and built in gear hub type. Derailleur type is a simple structure but it is vulnerable to external contamination and impact. And it is impossible to shift from the quiescent state. Built in gear hub type is very strong about the external contamination and impact because working part did not expose to the outside. In this paper, a new design of a continuously variable transmission with built in gear hub type for bicycles was developed and simulated. Stress and displacement analysis in built in gear hub by using finite element method were performed in order to develop improved structure of CVT.