An effective construction safety management system is required for reducing damage caused by construction site accidents. However, construction site safety management systems are mainly operated only at large scale, so there is a lack of safety management system that can be operated at a low cost even in smaller construction sites. In this paper, the authors propose an Internet of Things (IoT)-based construction site safety management system which can be operated at low cost not only at large construction sites but also at smaller construction sites. A prototype for the proposed system has been developed using a beacon technology, smartphone application, and sensors, Zigbee, WiFi, and LTE to monitor field workers and outsiders approaching the hazard zones at all times. The prototype system also provides danger alarm to safety managers in construction sites and at remote sites. It is expected that the developed system can effectively prevent safety accidents in large-scale and small-scale construction sites.