A gas processing apparatus of an embodiment includes: first and second dielectric substrates facing with each other; first and second discharge electrodes respectively disposed on a pair of facing principal surfaces of the dielectric substrates; first and second ground electrodes respectively disposed on a pair of principle surfaces at opposite sides of the principle surfaces of the dielectric substrates; a gas flow path to supply gas to be processed between the discharge electrodes; an AC power source to generate first and second plasma-induced flows by applying an AC voltage between the discharge electrodes and the ground electrodes; and a region disposed between the dielectric substrates at downstream of the plasma-induced flows from the discharge electrodes, and a gap between the dielectric substrates being 1.3 times or less of a sum of thicknesses of the plasma-induced flows.