To provide an apparatus for neutralizing PH of drainage which may be a small water tank and can efficiently neutralize and discharge high alkaline drainage in a short time.

The apparatus for neutralizing PH of the drainage comprises: a first line mixer 15 which is installed on a high alkaline drainage circulation path 14, and carries out first neutralization by mixing the high alkaline drainage with hydrochloride or sulfuric acid; a second line mixer 23 which is installed on a carbon dioxide treatment drainage circulation path 22 and completes neutralization by mixing the drainage subjected to the first neutralization treatment with carbon dioxide; and a discharge apparatus 24 for discharging the treated drainage outside of a carbon dioxide treating water tank 20.