The present invention relates to a highly efficient sodium hypochlorite generation apparatus capable of decreasing disinfection by-products, which is a chlorine disinfection device for on-site generation and produces sodium hypochlorite solution by electrolyzing sodium chloride aqueous solution on site, thereby requiring no additional liquefied chlorine storage equipment or disaster prevention equipment and securing flexibility of installation and operation while not being regulated by a high-pressure gas safety control act.The highly efficient sodium hypochlorite generation apparatus of the present invention capable of decreasing disinfection by-products comprises: a diaphragm electrolytic bath comprising an anode room into which a sodium chloride aqueous solution flows, a cathode room into which water flows, and a cation exchange membrane for dividing the anode room and the cathode room; an anode water storage tank for storing chlorine gas and anode water generated by the electrolysis of the anode room; a cathode water storage tank for storing sodium hydroxide generated by the electrolysis of the cathode room and discharging hydrogen gas; and a gas/liquid contact portion in which the chlorine gas supplied from the anode water storage tank reacts with the sodium hydroxide generated at the cathode water storage tank to produce sodium hypochlorite, wherein the sodium hypochlorite generation apparatus further comprises a water-splitting electrodialysis tank for producing hydrochloric acid and sodium hydroxide using a sodium chloride aqueous solution and water to supply the same as anode water and cathode water, respectively.The present invention can provide a highly efficient sodium hypochlorite generation apparatus capable of decreasing disinfection by-products which can minimize the generation of chlorate ions (ClO3−), by-products, by increasing the chlorine generation efficiency of an anode and adjusting a material balance in case of gas/liquid contact. In addition, since it is possible to provide chemicals generated using salt only to a diaphragm sodium hypochlorite generation apparatus, a highly efficient sodium hypochlorite generation apparatus capable of decreasing disinfection by-products with excellent safety and economic efficiency can be provided without using expensive chemicals that are difficult to handle.