Disclosed herein is an apparatus having a double wiper structure for sterilizing ballast water. Each wiper for use in removing foreign substances from an ultraviolet lamp has a double structure including a main wiper part and auxiliary wiper parts. The auxiliary wiper parts are disposed on opposite sides of the main wiper part so that when the wiper body is moved forward or backward, the corresponding auxiliary wiper part primarily removes foreign substances before the main wiper part wipes the ultraviolet lamp unit. Each auxiliary wiper part includes an inclined protrusion and a pointed part so that friction between the surface of the ultraviolet lamp and the auxiliary wiper part can be minimized. The main wiper part includes a first blade and a second blade that are respectively disposed on opposite sides of a depression formed in an inner circumferential surface of the main wiper part.