A gas introduction structure extends in a longitudinal direction of a processing container having a substantially cylindrical shape to supply gas into the processing container. The gas introduction structure includes an introduction section that partitions an introduction chamber, an ejection section that partitions a plurality of ejection chambers each including a plurality of gas holes through which the gas is ejected into the processing container, and a branch section that partitions a branch chamber connected to the introduction chamber. The branch chamber is branched to correspond to the number of ejection chambers in a tournament manner and connected to the ejection chambers.