Substrate processing apparatus and liquid mixing method

A substrate processing apparatus comprising:

• a mixing tank configured to mix a first liquid and a second liquid therein, the second liquid being mixed in an amount more than that of the first liquid;
• a first opening/closing valve configured to open/close a first flow path in which the first liquid flows;
• a second opening/closing valve configured to open/close a second flow path in which the second liquid flows;
• a first flow rate measuring unit configured to measure a flow rate of the first liquid flowing through the first flow path;
• a second flow rate measuring unit configured to measure a flow rate of the second liquid flowing through the second flow path;
• a control unit configured to control opening/closing of the first opening/closing valve and the second opening/closing valve;
• and
• a substrate processing unit configured to process a substrate by supplying a mixed liquid of the first liquid and the second liquid to the substrate,
• wherein, when an integrated value of the flow rate of the first liquid measured by the first flow rate measuring unit reaches a predetermined target value after the first opening/closing valve is opened, the control unit executes a first closing processing to close the first opening/closing valve, calculates a target value of an amount of the second liquid to be supplied to the mixing tank based on the integrated value of the first liquid flow rate from the opening of the first opening/closing valve to the complete closing of the first opening/closing valve, and executes a second closing processing to close the second opening/closing valve based on the calculated target value and an integrated value of the flow rate of the second liquid measured by the second flow rate measuring unit.