A ballast water treatment apparatus equipped with devices for injecting bromine salt and ozone, which is used to treat ballast water used in a ship, the ballast water treatment apparatus comprising: a ballast pipe into which seawater flows; a ballast pump for transferring seawater into the ballast pipe; a side-stream portion; bromine salt injection part; and an ozone processor, wherein the side-stream portion comprises a side-stream pipe, which is branched from the ballast pipe, for bypassing a portion of seawater introduced from the ballast pipe; a side-stream pump, which is installed in the side-stream pipe, for transferring a portion of seawater bypassed from the ballast pipe into the side-stream pipe; and an injector for injecting the bypassed seawater back into the ballast pipe, the bromine salt injection part comprises bromine salt storage tank for storing bromine salt; bromine salt transfer pipe, which is connected to the side-stream pipe, for injecting bromine salt supplied from the bromine salt storage tank into the side-stream pipe; and bromine salt injection pump, which is installed in the bromine salt transfer pipe, for pressurizing bromine salt to be injected into the side-stream pipe, and a diffuser for diffusing bromine salt so that bromine salt is sufficiently mixed with seawater, when bromine salt is injected into the side-stream pipe, wherein the bromine salt storage tank is located above a point where the side-stream pipe or the ballast pipe is connected to the bromine salt transfer pipe so that bromine salt is injected into the side-stream pipe or the ballast pipe by hydraulic pressure, and the ozone processor comprises an ozone injection device for supplying ozone to the side-stream pipe; a mixer, which is installed in the side-stream pipe, for mixing ozone supplied from the ozone injection device and seawater transferred into the side-stream pipe; and an ozone transfer pipe, which is connected to the mixer of the side-stream pipe, for injecting ozone supplied from the ozone injection device into the side-stream pipe. a ballast pipe into which seawater flows; a ballast pump for transferring seawater into the ballast pipe; a side-stream portion; bromine salt injection part; and an ozone processor, wherein the side-stream portion comprises a side-stream pipe, which is branched from the ballast pipe, for bypassing a portion of seawater introduced from the ballast pipe; a side-stream pump, which is installed in the side-stream pipe, for transferring a portion of seawater bypassed from the ballast pipe into the side-stream pipe; and an injector for injecting the bypassed seawater back into the ballast pipe, the bromine salt injection part comprises bromine salt storage tank for storing bromine salt; bromine salt transfer pipe, which is connected to the side-stream pipe, for injecting bromine salt supplied from the bromine salt storage tank into the side-stream pipe; and bromine salt injection pump, which is installed in the bromine salt transfer pipe, for pressurizing bromine salt to be injected into the side-stream pipe, and a diffuser for diffusing bromine salt so that bromine salt is sufficiently mixed with seawater, when bromine salt is injected into the side-stream pipe, wherein the bromine salt storage tank is located above a point where the side-stream pipe or the ballast pipe is connected to the bromine salt transfer pipe so that bromine salt is injected into the side-stream pipe or the ballast pipe by hydraulic pressure, and the ozone processor comprises an ozone injection device for supplying ozone to the side-stream pipe; a mixer, which is installed in the side-stream pipe, for mixing ozone supplied from the ozone injection device and seawater transferred into the side-stream pipe; and an ozone transfer pipe, which is connected to the mixer of the side-stream pipe, for injecting ozone supplied from the ozone injection device into the side-stream pipe.