This study focuses on the reaction characteristics of active hydrocarbon species mainly composed of methine radicals and active hydrogen species mainly composed of hydrogen radicals, to both of which methane as a raw material is converted by microwave irradiation to create plasma that comes into contact with the Pt/Al2O3 catalysis field. The results indicate that when 4 chemical species, i.e., active hydrocarbon species, active hydrogen species, acetylene molecules (produced by coupling of the active species) and hydrogen molecules are supplied to the solid catalyst, an increase in catalyst surface temperature facilitates apparent hydrogenation on the surface of the catalyst and thereby increases the yields of ethylene and ethane. It also appears that addition of hydrogen molecules to microwave-irradiated methane causes significant hydrogenation at 500 K or lower.