a support unit configured to support a substrate; and

a liquid supply unit configured to supply a treating liquid onto the substrate supported on the support unit, and

wherein the liquid supply unit comprises:

a tank configured to have an accommodation space for storing the treating liquid therein;

a circulation line configured to circulate the treating liquid stored in the accommodation space;

a supplementary line configured to supply the treating liquid to the accommodation space, and at which a valve is installed;

a heater installed at the circulation line, and configured to heat the treating liquid; and

a controller configured to control the valve, and

wherein the controller is configured to control the valve to perform a supplementary operation of supplying the treating liquid to the accommodation space through the supplementary line upon determining that a supplement of the treating liquid stored in the accommodation space is required, to control the valve to supply the treating liquid at a first average supply amount per unit time to the accommodation space while a first period of the supplementary operation is being performed, the first average supply amount averaged over an entirety of the first period, and to control the valve to supply the treating liquid at a second average supply amount per unit time to the accommodation space while a second period of the supplementary operation is being performed, the second average supply amount averaged over an entirety of the second period and different from the first average supply amount and

the first period happens before the second period.