An obstruction zone generation device (3) for a movable body (1) includes a calculation information generation module (31) to generate calculation information based on sensor information acquired by one or more information acquisition devices (2), an obstruction zone calculation module (32) to calculate an obstacle zone by target (OZT) for each target ship of one or more target ships (204a-204d) and generate OZT information, a mask area determination module (33) to determine for each target ship of the one or more target ships (204a-204d) whether to mask the OZT of the respective target ship in the OZT information based on a direction of the respective target ship and generate output information, and a display information generation module (34) configured to generate OZT display information for displaying the OZT of the one or more target ships (204a-204d) based on the output information and the OZT information.