To provide a gas feeder capable of controlling precisely a mass flow rate, in various kinds of supplied gases, without executing troublesome working for calibration and regulation.

In this gas feeder 1, a weight variation W of a material, i.e. an actual material consumption is measured by a weight measuring part 13, and a set mass flow rate Qmset set in a flow control part 6 is corrected to converge an actual mass flow rate Qm calculated based thereon toward a target mass flow rate Qmreq. The flow control part 6 is calibrated properly based on an actual material consumption weight. The mass flow rate is controlled with excellent reproducibility without executing periodically the working for the calibration and the regulation, and irrespective of the kind of handled supplied gas and control precision of the used flow control part 6.