To provide an underwater inspection device for inspecting in the water sealability of a base metal and a weld zone of a lining material without draining water in an underwater storage container for a spent fuel or the like.

An inspection box of this underwater inspection device has a seal packing, an ejector connection pipe and a negative pressure line on an opening end face. The ejector connection pipe is constituted of a high-pressure water supply pump and a supply source line through a water jet ejector, a water supply line and a water supply quantity adjusting valve. The water in the inspection box is sucked by the high-pressure water supplied from the water supply line on a place at the depth of water of 10m or more, and the inspection box is sucked onto the wall surface by a differential pressure with the pressure of pool water by depressurizing the inside of the inspection box. Leak water in a leak detection system provided on the lining type container back side is stopped by holding the inspection box in the sucked state onto an inspection object part in this way. Hereby, the existence of a weld zone penetration defect in the range of the lining material on an installation part is revealed by maintaining the inspection box.