Precast concrete structure increases because of its advantages such as enhancement of the productivity. Analysis by using finite element method has a possibility to make evaluation and design of precast concrete structure more reasonable. A reliable dynamic model of joint interface between precast concrete and site concrete is required for the analysis. This paper focuses the joint interface connected by deformed reinforcing bars. Experiment of element specimens representing the interface are conducted and numerical model for a relationship between shear force and shear displacement of the interface is proposed. Deformation of the reinforcing bar is regarded as combination of two arcs and established bond - slip models of the reinforcing bar are applied in the model. A simpler model for application to FE analysis, that is a bilinear slip - strain relationship based on the experimental curve, is also proposed.