To provide a method for executing a coherent jet technique method for flowing gas into liquid by efficiently using a single lance, and a system for executing the powder-pouring for feeding the powder into the liquid.

A surrounding flame 63 around a main gas flow continues to draw the surrounding gas in the coherent gas jet 62 and holds so as not to remarkably reduce the speed of the gas flow 62 for a desired gas flowing length and so as not to remarkably increase the diameter of the gas flow 62 until the gas flow 62 reaches a desired colliding position, e.g. the surface 64 of molten metal 65.