PURPOSE: A simple style water treatment apparatus for underground water is provided to evenly mix underground water and treatment liquid, to easily remove a foreign substance by collecting a foreign substance inside a water treatment tank with a collecting unit and discharging to outside, to reduce maintenance costs, and to be environmentally-friendly. CONSTITUTION: A simple style water treatment apparatus for underground water includes a water treatment tank(20), a treatment liquid supplying unit(50), a waterwheel unit(60) equipped in the water treatment tank, a stirring unit(90) equipped in the water treatment tank, a storage tub(10) connected with the water treatment tank, and an overflow pipe. The water treatment tank is supplied with underground water through a first supply pipe and a second supply pipe. The treatment liquid supplying unit supplies treatment liquid to underground water passing through the second supply pipe. The waterwheel unit is rotated by the fall of underground water flowing in through the first supply pipe and the second supply pipe. The stirring unit is connected to the waterwheel unit and stirs underground water. The storage tub stores underground water treated by the water treatment tank. The overflow pipe connects the water treatment tank with the storage tub and makes underground water overflowing from the water treatment tank flow into the storage tub.