Mechanical snubbers and inertia mass dampers are known as vibration control devices that have inertia mass elements and generate the inertial resistance force. By adding the devices with the inertia mass elements to piping systems, we aim to reduce various responses of piping systems subject to seismic disturbances. In this study, we propose a design method to optimize design parameters of inertia mass dampers installed on a piping system that is modelled by a 3-dimensional beam finite element model with some tangent and curved pipe elements to achieve good dynamic responses while maintaining the structural integrity of the piping system and the inertia mass dampers. A performance index considering various specifications related to mitigation of responses of the piping system for earthquake disturbances and the economic cost for installation of the devices with some inequality constraints is defined. Design parameters to optimize the performance index are the number and the model size (capacity) of the inertia mass dampers, the value of its inertia mass, and its placement (node and attitude) on the piping system of the inertia mass dampers. The performance index is optimized with a genetic algorithm. With a simulation study of a piping system represented by the 3-dimensional beam model, we show the effectiveness of the proposed design methodology.