Summary form only given. Due to globalization and increasingly competitive market environments, modern products must meet more requirements than ever before. They must not only be functional and aesthetically pleasing, but comfortable and ergonomic, as well. Consumers increasingly demand products that are easy to use and causes the minimum fatigue on the user side. Similar design elements are also becoming apparent in the design and layout of factory spaces. It is a now common for factories to adopt new ergonomic designs in order to reduce the possibility of dangerous situation and to increase the efficiency of interactions between workers and machines. These types of design activity that consider the effect of the products on the human body in the course of design are referred to as 'human-centered design'. Current CAD systems are unable to fully support a human-centered product design. Most of the research regarding ergonomic design has primarily focused on simple geometric analysis and simulation and has considered only the human model rather than the interaction between the product and the human model. As a result, it is difficult to apply the method to the traditional design process. Consequently, such designs are must be completed manually using trial-and-error iterative experiments on physical prototypes. This trial-and-error process is undesirable because it inherently requires human operators and their subjective evaluations. To overcome the limitations described above, an integrated environment that allows a simultaneous modeling of a product and a human user, simulation of both product and human behavior, and modification of the product based upon the simulation results. Therefore, the following topics will be discussed in this talk: 1. Unified environment for modeling both human body and product; 2. Human motion generation; 3. Integration with simulation software. Case study on the car interior design using the proposed approach will be also illustrate- d at the end of the talk.