NOVELTY - Three or more adsorption towers are filled with adsorption agent for carrying out adsorption separation of nitrogen from methane-containing gas. Nitrogen is adsorbed to adsorption agent in state which pressurized with respect to predetermined adsorption pressure. Nitrogen is disconnected from adsorption agent and regenerated under reduced pressure rather than the adsorption pressure. The pressure of pressure-reduced adsorption tower in recovery movement of adsorption process and recovery movement of regeneration process is more than the atmospheric pressure.    USE - Removal of nitrogen in methane-containing gas produced from underground.    ADVANTAGE - The method enables removal of nitrogen in methane-containing gas with high efficiency.    DETAILED DESCRIPTION - Three or more adsorption towers are filled with adsorption agent for carrying out adsorption separation of nitrogen from methane-containing gas as main component. Nitrogen is adsorbed to adsorption agent in state which pressurized with respect to predetermined adsorption pressure. Nitrogen is disconnected from adsorption agent and regenerated under reduced pressure rather than the adsorption pressure. The adsorption tower at pressure-reduced state is returned to adsorption pressure. Each process is switched in adsorption tower and implemented in each adsorption tower. The gas discharged from adsorption tower is pressure-reduced, when transferring to regeneration process from adsorption process is implemented. The recovery operation implements the recovery movement of high-pressure gas after adsorption, and recovery movement of low-pressure gas. The pressure of adsorption-tower pressure-reduced in recovery movement of adsorption process and recovery movement of regeneration process is more than the atmospheric pressure. An INDEPENDENT CLAIM is included for apparatus for removing methane-containing gas nitrogen.    DESCRIPTION OF DRAWING(S) - The drawing shows the schematic view explaining the removal of nitrogen in methane-containing gas. (Drawing includes non-English language text)