Provided is a tank sterilizer composed of a power supply part including an operation switch, and a sterilization part for sterilizing fluid in a tank, wherein a sterilization effect is maximized by generating microbubbles by electrolysis or electric discharge instead of killing bacteria by using a UV LAMP, an ozone lamp, and a pressure pump, and due to the coupling of a bubble generation module and a power connection module to each other by an electroconductive connector, a separate power connector is not required to be installed, whereby the tank sterilizer is simple in structure and is easy to be installed.