Workers in a construction site may be exposed various hazards and risks and may work with excessive demands beyond their physical abilities. It is important for construction companies to sustain a workforce in the work environment that does not sacrifice worker safety and health and maintains the required productivity. The purpose of this study was to develop a method for real-time estimation of the workload risk of individual workers at a construction site. Based on previous studies, we developed a workload model that includes behavioral information and physical characteristics of workers in addition to heart rate reserve (%HRR). Recent wearable devices have sufficient performance for measuring biological and physical load data without interfering from their work. In this case study, heart rate and physical activity were measured using smart wear equipped with a biosensor, an acceleration sensor and IoT system developed in our research. Using a logistic regression analysis as the statistical methods and SPSS as the analysis tool, we analyzed the risk caused by the workload. As a result, it became clear that the physical activity and the heart rate will be the important parameters for estimating workload risk in construction works. However, worker age and body mass index (BMI) did not have a significant effect on estimating workload risk. In the construction site, types of works and skills of workers will change according to the progress of the project. In order to ensure a stable workforce and productivity, it is necessary for construction industry to manage workers' health and safety. In conclusion of this paper, we propose that the real-time monitoring of heart rate and physical activity during construction work can be used for human resource management (HRM). With the development of this study, it will be possible to determine how the workers' workload affects productivity. It is believed that this research will be useful as an element of the integrated management technology of the entire construction site using ICT tools.