An aircraft control device determines, on the basis of relative positional relations between an individual aircraft and a target aircraft, a role of the individual aircraft with respect to the target aircraft, and a trajectory of the individual aircraft based on control operations determined according to the role of the individual aircraft. As an example, the aircraft control device represents the role of the individual aircraft with respect to the target aircraft as a numerical value and changes the role of the individual aircraft a plurality of times by changing the numerical value. Every time the role of the individual aircraft is changed, a minimum distance to target is calculated for the individual aircraft, and the role of the individual aircraft having the largest minimum distance to target is determined as the role of the individual aircraft.