A liquid supply apparatus is provided. The liquid supply apparatus includes: a base unit having an operating space, an inlet port, through which a treatment liquid is introduced, and an outlet port, through which the treatment liquid is discharged, formed therein; bellows having the operating space formed on its outside within the base unit, including an inlet and an outlet, which form ends of the inlet and outlet ports, respectively, of the base unit and communicate to create a storage space that the treatment liquid flows in and out of, and expanding or contracting to increase or reduce the volume of the storage space; an operating unit supplying operating fluid into or discharging the operating fluid from the operating space; and a drain line communicating with the storage space, from below the base unit, and discharging the treatment liquid, wherein the operating unit supplies the operating fluid into the operating space to enable the bellows to contract, or discharges the operating fluid from the operating space to enable the bellows to expand, and the drain line discharges residual treatment liquid remaining in the storage space to replace the treatment liquid.