In the present study、 reaction tests were undertaken with the goal of removing the calcium ions that cause scaling in the mother solution used for salt making. First、 caustic soda and carbon dioxide gas were added to seawater-based brine that had been concentrated by electro-dialysis with an ion-exchange membrane. This technique allows calcium ions to be selectively removed from the brine. The calcium ion concentration decreased to 0.002 mol/L. Then、 the amount of sodium hydroxide required is 0.2 mol per 1 L of brine. The amount of carbon dioxide that can be captured is 0.10 g per 1 g of salt produced. Then the ratio of aragonite in the sludge increased with a decrease of the sodium hydroxide addition rate and an increase of the carbon dioxide addition rate. So it is thought that the ratio of aragonite accelerates by a low in local super-saturation. Next、 the brine from which the calcium ions had been removed was evaporated. No calcium scale precipitate was observed as a result of the evaporation process. The effect on sodium yield of the salt-making evaporator was minimal.