An aircraft includes a vessel checker, an image generator, an appearance determining unit, and an information transmitter. The vessel checker identifies a suspicious vessel candidate by comparing a marine vessel detected by a marine search radar with a marine vessel transmitting data with an automatic identification system. The image generator generates an image by photographing the suspicious vessel candidate after the aircraft approaches the suspicious vessel candidate in accordance with a route for approaching the suspicious vessel candidate. The appearance determining unit determines whether the suspicious vessel candidate in the image has an appearance characteristic of a suspicious vessel. The information transmitter transmits, to an external apparatus, information indicating that the suspicious vessel candidate has the appearance characteristic of the suspicious vessel if the suspicious vessel candidate has the appearance characteristic of the suspicious vessel.