To provide a gas decomposing apparatus the gas decomposing efficiency of which is increased by arranging a rotary electrode to form an apparent plasma discharge plane in the gas fluidizing space between a cylindrical body and a shaft, in which the amount of the gas to be decomposed can be controlled and the pressure loss of which is made low.

This gas decomposing apparatus is composed of the cylindrical body 1 combining the second electrode, the shaft 2 arranged coaxially in the body 1, a rotator 3 (a rotating means) for rotating the shaft 2, the space 4 between the body 1 and the shaft 2 where the gas being the matter to be treated is fluidized, the rotary electrode 5 being the first electrode fixed to the shaft 2 rotated by the rotator 3 to be projected into the space 4 and a power unit 6 for applying a potential difference between the electrode 5 and the body 1 combining the second electrode to generate a plasma discharge in the space 4.