A gas processing apparatus comprising: a plasma equipment (20A, 20B) series having a plurality of units of plasma equipment arranged in series on a gas flow channel; a gas introduction section for introducing gas into the plasma equipment series; a first gas sensing section for measuring gas that passes through the gas introduction section; a gas transfer section for transferring the gas processed by one plasma equipment unit to the other plasma the equipment unit; a control means (12A, 12B) that controls the operation of each of the units of plasma equipment of the plasma equipment series, selects the number of units of plasma equipment to operate according to a component of the introduced gas, and determines the number of units of plasma equipment to operate on the basis of an input from the first gas sensing section; wherein: each of the units of plasma equipment comprises: (i) a plasma generator for generating plasma within a reaction chamber communicated with the gas flow channel; (ii) a microwave radiator for radiating microwaves to the plasma generated by the plasma generator; and (iii) a cavity defined by a cylindrical wire mesh open at one end and provided with an opening at the other end, and a conductive lid joined to the open end of the wire mesh, for surrounding at least one reaction chamber and forming a resonance cavity for electromagnetic waves. a plasma equipment (20A, 20B) series having a plurality of units of plasma equipment arranged in series on a gas flow channel; a gas introduction section for introducing gas into the plasma equipment series; a first gas sensing section for measuring gas that passes through the gas introduction section; a gas transfer section for transferring the gas processed by one plasma equipment unit to the other plasma the equipment unit; a control means (12A, 12B) that controls the operation of each of the units of plasma equipment of the plasma equipment series, selects the number of units of plasma equipment to operate according to a component of the introduced gas, and determines the number of units of plasma equipment to operate on the basis of an input from the first gas sensing section; each of the units of plasma equipment comprises: (i) a plasma generator for generating plasma within a reaction chamber communicated with the gas flow channel; (ii) a microwave radiator for radiating microwaves to the plasma generated by the plasma generator; and (iii) a cavity defined by a cylindrical wire mesh open at one end and provided with an opening at the other end, and a conductive lid joined to the open end of the wire mesh, for surrounding at least one reaction chamber and forming a resonance cavity for electromagnetic waves. (i) a plasma generator for generating plasma within a reaction chamber communicated with the gas flow channel; (ii) a microwave radiator for radiating microwaves to the plasma generated by the plasma generator; and (iii) a cavity defined by a cylindrical wire mesh open at one end and provided with an opening at the other end, and a conductive lid joined to the open end of the wire mesh, for surrounding at least one reaction chamber and forming a resonance cavity for electromagnetic waves.