Gas supply system, plasma processing apparatus, and gas supply method

The invention relates to a gas supply system, a plasma processing apparatus, and a gas supply method. A control unit provided in a gas supply system executes: a control for calculating the flow rate of a main gas flowing through each of a plurality of gas supply flow paths; acquiring the flow rate of the additive gas flowing in the additive gas flow path and mixed with the main gas flowing in each of the gas supply flow paths; calculating a total flow rate, which is the sum of the flow rate of the main gas and the flow rate of the additive gas, in each of the plurality of gas supply flow paths; a calculation unit for calculating the internal pressure of each of the plurality of gas supply flow paths by using the total flow rate calculated in each of the plurality of gas supply flow paths and the relationship between the flow rates and the pressures of the main gas and the additive gas acquired in advance; calculating the ratio of the internal pressure calculated in each of the plurality of gas supply flow pat