Substrate processing apparatus and substrate processing method

A substrate processing apparatus includes: at least one processing part for etching a polysilicon film or an amorphous silicon film formed on a substrate using an alkaline chemical liquid; a reservoir configured to recover and store the chemical liquid used in the at least one processing part; processing lines configured to supply the chemical liquid stored in the reservoir to the at least one processing part; a circulation line configured to take out the chemical liquid from the reservoir and to return the same to the reservoir; and a first gas supply line connected to the circulation line and configured to supply an inert gas to the circulation line. The circulation line includes an ejection port configured to eject a mixed fluid of the inert gas supplied by the first gas supply line and the chemical liquid taken out from the reservoir into the chemical liquid stored in the reservoir.