To provide a delivery method of a gas to be treated to a decomposition treatment device which enables variably quantitatively determining and supplying the gas to be treated containing a halogen-containing compound in accordance with an intra-temperature of a reaction tube, and stably supplying of the gasified halogen-containing compound into the reaction tube, without regasification of the gasified halogen-containing compound, and a decomposition treatment device.

This decomposition treatment device 10 is equipped with a tubing pump 78 for delivering the gas to be treated which is obtained by gasifying the liquid halogen-containing compound, in a variably quantitatively determinable manner, to the reaction tube 20 in accordance with the internal temperature of the reaction tube 20. In addition, a partial pressure setting device 90 is arranged in a pipeline 84 between the tubing pump 78 and the reaction tube 20.