This paper presents a method to generate an aesthetic surface which is represented by two guide curves and a curve-ruler. A curve-ruler is an expression of a ruler whose curvature variation is monotone and aesthetic, and it is a mathematical version of the actual ruler used in the automotive industry. A ruler-surface is a surface which is a locus of the curve-ruler moving along two guide curves. First, a generation procedure of a guide curve and conditions for producing an aesthetic surface are described. Then, a ruler-surface is formulated parametrically according to the movement of the ruler along two guide curves. Examples of ruler-surfaces show that this method can generate surfaces with different characteristics by various kinds of curve-rulers. Modeling examples are presented indicating that the method could be a supportive system for designer/s intuitive work.