Considering the effect of the interaction between piping and support systems in the piping design is a more integrated approach to improve the reliability of piping systems. So, it is important to clarify the dynamic characteristics of the piping and the restraint structure during the seismic events. It may be desirable to investigate the effect of the gap on the response and the local stress of the piping systems. The dynamic characteristics of a simplified piping model with gaps was investigated by the tests and the analysis. Three-dimensional piping model test was performed to estimate the effect of the gap on the response of the piping system. It can be found that the local stress and the stiffness of the piping and the restraint structure under the seismic loadings should be considered in the seismic design. The gap size was not so effective on the response of the 3-dimensional piping system in the high-level response.