A submersible that can be easily transported due to a reduced weight of the submersible is provided, and a submersible that is easy to operate and safe is provided. A submersible according to the invention is designed so that a cabin for boarding an operator has a size just enough to accommodate the operator and even such a light weight of the submersible can cause the submersible to submerge. Furthermore, when an operator having a weight smaller than a design maximum operator's weight of the submersible is on board and therefore the total weight of the submersible is reduced and the buoyancy thereof is increased, the buoyancy of the submersible is adjusted by pouring water having a weight corresponding to a difference between the design maximum operator's weight and the actual weight of the operator into an expansion container, disposed in the cabin, capable of expanding by containing water. In this manner, the net weight of the submersible is prevented from increasing.
