NOVELTY - Method for concentrating methane gas involves performing pressure swing adsorption cycle. The pressure swing adsorption cycle involves repeatedly and sequentially carrying out (a) providing adsorption columns (A1,A2,A3,A4) respectively filled with adsorbent (A11-A41), (b) adsorption process, (c) primary pressure-equalizing process, (d) pressure-reducing process, (e) secondary pressure-equalizing process, and (f) pressure-rising process. The adsorbent is capable of adsorbing methane gas contained in air in high-pressure state of atmospheric pressure vicinity.    USE - Method for concentrating methane gas (claimed).    ADVANTAGE - The method enables concentration of methane gas with effective usage of hardly-recyclable coal-mine gas, and provides highly-concentrated methane gas.    DETAILED DESCRIPTION - Method for concentrating methane gas involves performing pressure swing adsorption cycle. The pressure swing adsorption cycle involves repeatedly and sequentially carrying out (a) providing adsorption columns (A1-A4) respectively filled with adsorbent (A11-A41), (b) adsorption process, (c) primary pressure-equalizing process, (d) pressure-reducing process, (e) secondary pressure-equalizing process, and (f) pressure-rising process. The adsorbent is capable of adsorbing a methane gas contained in air in high-pressure state of atmospheric pressure vicinity, and removing methane gas in which adsorbent is adsorbed in a low-pressure state. The different pressure states are set as intermediate pressure states for the internal pressure of each of the adsorption columns (A1-A4). The adsorption process involves discharging off gas comprising air as a main component from adsorption-column upper portion while receiving methane-containing gas in high-pressure state of the atmospheric pressure vicinity from the adsorption-column lower portion, and adsorbing methane gas at the adsorbent. The primary pressure-equalizing process involves respectively transporting gases in the adsorption columns (A1-A4), each of which is in a high-pressure state, to upper portions of another adsorption columns (A1-A4) each of which is in an intermediate-pressure state having pressure less than in each of the upper sides of the adsorption columns (A1-A4) to change the pressure in each of the adsorption columns (A1-A4) to a pressure of a high-pressure-side intermediate-pressure state. The pressure reduction process involves pressure-reducing the adsorbent to a low-pressure state, removing methane gas in which the adsorbent is adsorbed, and collecting methane gas from the adsorption-column lower portion after column internal pressure reduces with respect to a primary pressure-equalizing process. The secondary pressure-equalizing process involves respectively transporting the gases in the adsorption columns (A1-A4), each of which is in high-pressure-side intermediate-pressure state having a higher pressure than in the low-pressure state, to another adsorption columns (A1-A4) each of which is in a low-pressure state to change the pressure in each of the adsorption columns (A1-A4) to a pressure of a low-pressure-side intermediate-pressure state. The pressure-rising process involves selectively decompressing methane gas to the high-pressure state for adsorbing adsorbent further, after raising a column internal pressure according to a final pressure-equalizing process. Air is supplied for rising pressure from adsorption-column upper portion in the adsorption column.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of methane concentration apparatus. (Drawing includes non-English language text)    Supply portion (1)    Discharge portion (2)    Adsorption columns (A1,A2,A3,A4)    Control apparatus (C)    Raw material gas holder (T1)