It is detected of an interference between feeder links of communication relay apparatus, which tends to occur when the number of movable aerial-floating type communication relay apparatus increases in a same area. Plural feeder-link model elements are generated with respect to the plural communication relay apparatuses, wherein each of which a feeder-link receiving point corresponding to a position of the communication relay apparatus, a feeder-link transmitting point corresponding to a position of a gateway station, and a line segment connecting the feeder-link receiving point and the feeder-link transmitting point to each other in a three-dimensional space model. An occurrence of interference between feeder links is determined based on distances between the line segment and the feeder-link receiving point among feeder-link model elements different from each other on the three-dimensional space model.