There is provided a fall-into-water accident determination system including: a weight detector configured to be attached to an occupant of a vessel and configured to detect a weight applied to a foot of the occupant; a water detector configured to be attached to the occupant and configured to detect water; and a fall-into-water accident determinator configured to determine whether a fall-into-water accident in which the occupant falls into water from the vessel occurs. The fall-into-water accident determinator determines whether the weight changes based on a detection result of the weight detector. The fall-into-water accident determinator determines whether the occupant is immersed in water based on a detection result of the water detector. And the fall-into-water accident determinator determines that the fall-into-water accident occurs when the weight changes and the occupant is immersed in water.