As the proportion of older adults increases globally, raising healthy life expectancy is becoming an urgent issue. To address this, shifting the medical system from conventional disease treatment to disease prevention, early diagnosis, and early treatment is desirable. It is necessary to utilise digital technologies not only to acquire and visualise health-related data, but also to link it to people’s behavioural changes. However, there is a limit to the extent that individuals can change their behaviour and maintain their health through their own efforts. A social system is required to achieve behavioural changes with the support of the surrounding environment. This should be a platform service encompassing various stakeholders. In this study, we perform a system design on how to construct a behavioural change platform (BCPF) service to promote behavioural changes based on the support of the surroundings, and how to make it into a platform service. First, the system structure of the BCPF service is described using object process methodology to identify main objects, processes, and system boundaries. Second, customer value chain analysis is conducted to identify the primary value streams among service providers and users of the BCPF service as stakeholders. Finally, the number of BCPF service users over time is simulated using system dynamics. We find that the number of BCPF service users effectively increases by improving vital data which directly related to the reduction of the morbidity rate of target diseases and by conducting appropriate promotions that lead to the reputation of this service.