The demand for Graphical User Interface (GUI) applications has witnessed an increase. However, it is difficult to develop such GUI applications, because their structures are complicated. Therefore, we propose an approach for the automatic generation of GUIs for the purpose of facilitating GUI applications' development from dialog description. These dialogs are described using a Petri net which includes GUI information. A special-purpose Petri net editor is developed for this purpose, so system designers can work in an environment which is suitable for developing GUI applications. The most important feature of this system is as follows: after generating GUI application, users can customize the detailed size and arrangement of widgets to suit the user's needs. This customization does not require the use of any special software tools. In this research, we assumed that GUI application development is divided into three roles, system designers who are in charge of dialog description, graphic designers who are in charge of the customization of GUI, and application programmers who are in charge of programming of applications. The system designers describe the dialog, then the graphic designers and application programmers work independently or simultaneously.