A powder supply device 1 includes a powder feed pipe, at least part of which is an expansion/contraction part, a load cell, a pressure indicator, and a controller, wherein the controller obtains a powder weight or a rate of change in powder weight in the feed tank by using a value obtained by subtracting a value proportional to the pressure in the expansion/contraction part from the load applied by the feed tank to the load cell and adding a value proportional to a rate of change in pressure in the expansion/contraction part, and controls the flow rate of the powder to be fed to the outside of the feed tank by using the powder weight or the rate of change in powder weight.

A discharge flow rate of a loss-in-weight scale is controlled by continuously changing control outputs to save the time necessary for data stabilization. A curve relating the discharge flow rate and the control output is obtained by using the functional relationship between the control output and time and the functional relationship between the material weight and time. The discharge flow rate can be precisely controlled by directly selecting or inputting a value of the control output, to achieve the objectives of direct controlling and of avoiding the time for data stabilization.