To provide a treatment method and treatment apparatus of circulation type cooling tower blow water, for allowing an electrode type water gauge of a cooling tower to surely sense a water level and stably functioning as a treatment system, by preventing the rise of purity and the decline of electric conductivity of makeup water that is supplied to the cooling tower and recycled.

A treatment method of circulation type cooling tower blow water includes: a suspended matter removing step of removing suspended matter from cooling tower blow water from a circulation type cooling tower provided with an electrode type water gauge by a clarifier and obtaining clarified water; a desalting step of desalting a part of the clarified water and obtaining desalted water; a makeup water recovery step of mixing a part of the clarified water and the desalted water and recovering it as makeup water; a circulation step of supplying the makeup water to the cooling tower to recycle it; and a step of adjusting the electric conductivity of the makeup water to be a sensing lower limit value of the electrode type water gauge or higher by adjusting the receiving amount of the desalted water and/or the clarified water to a makeup water tank.