A door for a vehicle is assembled by joining three modules together to facilitate the assembly process. The three modules are an outer module including an outer panel, a window regulator module including a window pane and a window regulator, and an inner module including an interior member. The window regulator module is preliminarily assembled as an independent unit, so that it is easy to adjust the open and closed positions and the movement of the window pane. These modules are joined by fastening means extending along the direction of the thickness of the door, so that the assembly operation is made easier.
