The purpose of this research was to develop an integrated interface for the usability test of systems or products in the design process. It is capable of automatically creating GOMS models which can predict human task performances. It can generate GOMS models to be interacted with the prototype interfaces. It can also effectively manage various design information and various usability test results to be implemented into the new product and/or system design. Thus we can perform usability test for products or system prototypes more effectively and also reduce time and effort required for this test. For usability tests, we established an integrated interface based on GOMS model by the LabVIEW program. We constructed the system that the linkage to GOMS model is available. Using this integrated interface, the menu structure of mobile phone can be constructed easily. User can design a depth and a breath that he want. The size of button and the label of the button is changable. The path to the goal can be defined by the user. Using a designed menu structure, the experiment could be performed. The results of GOMS model and the actual time are presented. Besides, values of operators of GOMS model can be defined as the value that user wants. Using the integrated interface that we developed, the optimal menu structure deducted. The menu structure that user wants can be established easily. The optimal layout and button size can be decided by comparison of numerous menu structures. User can choose the method of usability test among GOMS model and empirical data. Using this integrated interface, the time and costs can be saved and the optimal menu structure can be found easily.