A machinery design process is proposed based on the routine design of machine elements. The routine design knowledge on each machine element, decribed in handbooks or catalogs, is represented in a machine readable form as a design pattern. The designer describes the product design in terms of design patterns placed in the work space and the constraints between them. The shapes of each machine element is detailed by the system in accordance with the design knowledge in design patterns and the constraints in the product design representation. The design knowledge in a design pattern consists of a set of parameters to represent requirements for the machine element, the parametric representations of parts' shapes that construct the machine element, and the knowledge for detailing shapes. Each design pattern deal with positions of parts that are related to the machine element. The complete geometric model of each part is generated by connecting the portions detailed in accordance with several design patterns. A prototype system has been implemented on an object oriented language, and some design examples are shown.