In this paper, a parametric design method for aesthetic shapes which provides a direct and interactive modeling is presented. As used in an actual automobile design, our method utilizes a curve-ruler to create a free-form surface. In order to construct a surface, a curve-ruler is defined by a function like a polynomial at first. And then, two guide curves are generated by Bézier curves. Moving a curve-ruler on guide curves, a free-form surface is obtained as its locus. Designer only designates a type parameter of the curve-ruler and the parameters to allocate the curve-ruler on the guide curves. To construct a whole shape of a product, we introduce another set of parameters to control an outer shape. In this way, it is possible to control the local surface and the global shape independently. Moreover, the methods to generate a fillet, trimmed surface and features are presented. We have implemented a prototype system and will demon-strate its application on an automobile.