Framework for natural behavior interface design based on a triadic representation of action from Engeström's activity system

User-centered thinking is incorporated into many contemporary design practices. However, some practices may lack a thorough consideration of the user-product relation during the product development. This paper introduces natural behaviour interface through a theoretical approach to the activity system, for the purpose of facilitating a more natural subconscious interaction between the user and the product. It first presents an analysis of activity theory and activity-centered design to identify their constituent elements and to understand the nature of design focused on user-product focused design: affordance design and natural behavior interface design, through case analyses. Ultimately, the paper aims to introduce a natural behavior interface design framework as an effective means of correlating a product"s main operation with the user"s natural behaviour and thus closing the gap between the subject, mediating artifacts and the object. Furthermore, a product that considers natural behaviour interface as a higher chance of triggering the user"s emotion, can foster the user"s deeper attachment to the product.