Disclosed is a method of adjusting a concentration of a chemical liquid in a treatment liquid, the method including: treating a substrate by supplying a treatment liquid stored in a main tank from a nozzle in a heated state to the substrate, and recovering the treatment liquid used in the treatment of the substrate to the main tank directly or via still another tank, and then reusing the recovered treatment liquid, a concentration adjustment operation of adjusting a concentration of the treatment liquid in the main tank is performed in a standby time period in which the substrate is not treated with the treatment liquid, and the concentration adjustment operation is performed by discharging the treatment liquid in a heated state from the nozzle to evaporate a part of the diluting solution, and recovering the discharged treatment liquid to the main tank.