A flight information acquisition unit repeatedly acquires the respective flight status of a plurality of drones in flight. A flight irregularity determination unit determines whether or not the drones are flying in a manner deviated from a flight plan. When a flight status of a drone indicating flight deviated from the flight plan has been acquired, a first collision specification unit specifies the drone at risk of collision with a drone having that flight status. When a flight status indicating that there is a possibility of crash for a drone has been acquired, a flight status processing unit (such as a flight irregularity determination unit) sets a higher priority for processing based on the flight status acquired from that drone than for processing based on the flight status acquired from another drone.