In a raw material gas supply apparatus, a control unit obtains an offset value of (m3−(m1+m2)), m1, m2 and m3 being respective measurement values of first and second mass controllers, and a mass flow meter, by supplying a carrier gas and a dilution gas in a state where the carrier gas flows through a bypass channel. Further, the control unit obtains an actual measurement value of a flow rate of the raw material by subtracting the offset value from (m3−(m1+m2)) obtained by supplying the carrier gas and dilution gas in a state where the carrier gas flows through the inside of a raw material container and calculating a difference between a target value of the flow rate of the raw material and the actual measurement value, and adjusts a set value of the first mass flow controller such that the flow rate of the raw material becomes.