To provide an inundation preventing machine which can immediately cope with sudden abnormal flood and positively shields a ventilation hole of an underground structure with a small driving force.

According to the inundation preventing machine for the ventilation hole 30 of the underground structure, a shutter member is arranged in an opening 31 surface of the ventilation hole 30, such that the shutter member is drawn in a direction that tilts toward a downstream side of flow of the inundation, to thereby openably close the ventilation hole 30.