Substrate processing apparatus and substrate processing method

A substrate processing method executed by a substrate processing apparatus including:

• a retaining tank that retains therein processing liquid;
• a circulation line that returns, to the retaining tank, the processing liquid delivered from the retaining tank;
• a supply line that connects the circulation line to a supply unit that supplies the processing liquid to a substrate;
• a returning line that is connected to the supply line to return the processing liquid from the supply line to the retaining tank;
• and a flowmeter and a constant-pressure valve that are provided on the supply line on an upper flow side than a connecting portion of the returning line and the supply line, the method comprising:
• during a waiting time interval in which the processing liquid is caused to flow into the returning line not to supply the processing liquid from the supply unit to the substrate, calculating an opening degree of the constant-pressure valve in supplying the processing liquid to the substrate based on a measurement value of the flowmeter and an opening degree of the constant-pressure valve;
• and
• during a supplying time interval in which the processing liquid is caused to flow into the supply unit to supply the processing liquid to the substrate, setting an initial opening degree of the constant-pressure valve to the calculated opening degree.