To provide a sterilization method of bath water and a sterilization device thereof which is practical notwithstanding the simple constitution without using an electric source.

This sterilization device 1 is water-passable into a casing 2 and is provided with a cathode 3 comprising base metal in the galvanic corrosion and an anode comprising noble metal in the galvanic corrosion via a spacer 6a. This sterilization device 1 is immersed in the bath water, thereby, an electromotive force ≥0.7 volt is generated between both electrodes, the sterilization of the bath water between them is made possible, the bath water is ceaselessly circulated in the sterilization device 1 by free convection and, thereby, the whole of bath water can be sterilized. The sterilization device 1 is provided with a positioning means such as a sucking disc 13 and a filtration part 5. Therein, when both of the electrodes are vertically disposed so as to face oppositely, the water passing between them is made possible and, therefore, this sterilization method and device is made practical even when both of the electrodes themselves have not a water-passable structure.