A position of a target ship alongside is displayed in animation on a display unit 17 by the computer 11 based on any one of the positional information on the target ship alongside, which is transmitted from an automatic identification system (AIS) of a target ship alongside and is obtained by an AIS communication unit 13, positional information on the target ship alongside, which is obtained by the GNSS communication unit 14 from a global navigation satellite system, and positional information on the target ship alongside, which is manually inputted via an operation unit 18. Therefore, the latest position of the target ship alongside can be always displayed in animation.