To decrease energy to be charged for progressing a reaction when producing a useful gas.

The apparatus for producing the gas comprises a reaction column 1 forming a passage 2 of a gaseous reactant, a solid catalyst 4 arranged in the passage 2, a first electrode 3 and a second electrode 5 which is a counter electrode of the first electrode 3. The first electrode 3 together with the second electrode 5 generates low-temperature plasma at the vicinity of the surface of the solid catalyst 4, and the Low-temperature plasma produces a product material by exciting the gaseous reactant. The same material as the solid catalyst used when producing the product material without using the plasma is used as the solid catalyst. The first electrode 3 is arranged on the wall in the inside of the reaction column 1, and the second electrode 5 has a rod shape and arranged at the center of the passage 2. The solid catalyst 4 is covered with the first electrode 3.