In recent years, the use of unmanned aerial vehicles, including drones, to conduct inspections has been attracting increasing attention. When a drone is used for inspections, it often approaches objects and obstacles, and its collision risk increases the closer it gets. In this study, we developed an omnidirectional proximity sensor system for drones using optical time-of-flight (ToF) sensors to avoid collisions. The sensor system consists of 87 ToF sensors that can estimate the distance between the sensors and objects. The ToF sensors are mounted on both the propeller guard of the drone and its body. Thus, they can measure objects horizontally, at ±45 • Z direction, and above the drone. Further, the sensor system can detect objects around the drone in a noncontact area. Accordingly, the drone can be controlled using the measured data. Our results show that drones using the proposed sensor system can avoid unexpected contacts and collisions during flights. Consequently, we believe that the sensor system will be highly useful in drone operation.