On the basis of illuminance acquired by an acquisition unit (11), a prediction unit (14) predicts an illuminance limit time (LT) at which the illuminance in an area where a drone (10) flies will be less than a threshold value, and predicts the remaining time (ST) from the present time (NT) to the illuminance limit time (LT). In accordance with the above-mentioned method, a comparison unit (15) compares the remaining time (ST) predicted by the prediction unit 14 with a future scheduled flight time (FT) in flight plan information of the drone (10). When the remaining time (ST) is considered to be insufficient with respect to the future scheduled flight time (FT), a changing unit (16) changes the flight plan information of the drone (10) so that the future scheduled flight time (FT) falls within the remaining time (ST).