A treatment liquid supply device and a wet treatment device with which an extremely small quantity of the treatment liquid can be accurately supplied, as a method for supplying a treatment liquid to an extremely small wafer of half inch size, including: a syringe that sucks and discharges the treatment liquid; a treatment liquid bottle that is filled with the treatment liquid; a suction hose that has one end connected to the treatment liquid bottle and the other end connected to the syringe, and sucks the treatment liquid inside the treatment liquid bottle to the syringe; a supply hose that has one end connected to an intermediate section of the suction hose and serves to supply, to the surface of the wafer, the treatment liquid discharged by the syringe; and a three-way solenoid valve that controls opening/closing of each of the suction and supply hoses.