To economically and efficiently obtain a natural salt by installing an outer wall and a water reservoir on aslant cement concrete floor, allowing seawater to thinly adhere to the floor, and then evaporating the seawater by the aid of solar heat or the atmosphere.

First, a cement concrete floor is slantly laid, a water reservoir is provided on the lower part of the inclined floor, and an outer wall on the other edge. Secondly, seawater is allowed to thinly adhere to the floor, and evaporated by the aid of solar heat or the atmosphere. Thirdly, seawater is allowed to flow from the top of the floor, and then flows through the surface of the floor and thinly adheres thereto, the rest of the seawater being accumulated in the reservoir. The seawater on the surface of the floor is immediately evaporated on its exposure to solar heat or the atmosphere; on drying, additional seawttter is allowed to flow again. Thus, because of repeated seawater casting and evaporation to dryness, the seawater on the surface of the floor repeats crystallization and crystal melting, resulting in higher salt concentration of the seawater accumulated in the reservoir and therefore facilitating salt crystal deposition. For the floor, a multi-tiered design with slab structure increases land area, being effective in terms of mass production of the aimed sea salt. Furthermore, installation of a detachable cover and a roof enables the aimed sea salt to be produced without hindrance of any rainfall.