The invention relates to a treatment gas supplying mechanism, supplying method and gas treatment device, wherein the treatment gas supplying mechanism supplies treatment gas for making the treatment container at preset pressure in short time. The treatment gas supplying mechanism (3) comprises: a He
gas supply resource (30) for supplying
helium gas as treatment gas to a chamber (2) as treatment container of holding substrate; a treatment gas
jar (33) for temporarily storing
helium gas from the He
gas supply resource (30); a treatment gas circulating parts (35) for supplying
helium gas from the He
gas supply resource (30) to the treatment gas
jar (33) and supplying the
helium gas from the treatment gas
jar (33) to chamber (2), wherein the
helium gas is temporarily stored in the treatment gas jar (33) from the He gas supply resource (30) through the treatment gas circulating parts (35) and supplied to the chamber (2) from the treatment gas jar (33).