To prevent the generation of precipitation even at a low temperature although an effective component is contained in a high concentration.

A method for producing liquid salt for a special purpose includes a concentration process in which a part of fresh water is separated from seawater to prepare a concentrated solution, a desalting potassium-removing process in which the concentrated solution obtained by the concentration process is heated and desalted to obtain a desalted potassium-removed concentrated solution, and a magnesium-removing process in which the desalted potassium- removed concentrated solution obtained by the desalting potassium-removing process is added with potassium hydroxide to be mixed, and magnesium contained in the solution is precipitated as magnesium hydroxide to remove magnesium.