The nut is one of the mechanical binding elements for the purpose of mechanical structure. But the weak point of the nut is that the binding force can be loosened due to various kinds of mechanical vibration. In this thesis, the new locknut is researched and developed to overcome the weak point of the existing nut. There is a spring inside of the locknut, which induces the pressure to the teeth of the screw by elastic force of spring and prevents unlocking of the mechanical structure. Therefore, by applying the locknut which comes out of this study to the mechanical structure, we can obtain not only the credibility of the products, but also the cost down through reducing the number of working process steps.