This paper proposes a feature modeling method which realizes a product model in the computer according to the designer's intent and modifies its shape directly according to the change of dimensional parameters. The designer's intent is represented as topological and geometrical constraints, which the designer specifies explicitly or implicitly with the shape properties, position and size of a feature. Direct modification of features is realized with a swept volume generated locally instead of the reevaluation of a history of feature operations which is used in the current parametric modeling systems. This enables efficient and unambiguous parametric modeling by detecting inconsistency between topology and geometry. The product model composed of a feature model and a geometric model is expressed with face-based representation and processed symbolically in an algebraic computation system. The algorithms of the feature generation and modification are described and their examples are shown.