A manufacturing method is provided for producing a carbon material adsorbing nitrate nitrogen, nitrate nitrogen or a fluoride ion through an ion exchange with a chloride ion. Plant material can be impregnated with a calcium chloride solution. Subsequently, the plant material can be carbonized to enable the plant material to support chloride ions that can provide ion exchanging capability with nitrite nitrogen, nitrate nitrogen, and a fluoride ion via calcium. The temperature of the carbonization permits the deposits of a calcium chloride compound within 2% to 25% by weight as a functional group in a carbonized material having ash components.