subjected to water treatment the crude gas from which ammonia and hydrocarbons have been removed is exhausted from the top of the washing tower 303 and introduced into the acidic gas absorption tower 101 the acidic gas absorption tower 101 separates and removes acidic gases particularly h 2 s in the crude gas by a physical absorption process a solvent is supplied into the acidic gas absorption tower 101 and absorbs acidic gas in the crude gas the crude gas from which acidic gases have been removed is exhausted from the top of the acidic gas absorption tower 101 and is introduced into the solvent absorption tower 306 the solvent after the acidic gas absorption is discharged from the bottom of the acidic gas absorption tower 101 and is heated in a heat exchanger 103 by the solvent regenerated by the acidic gas stripping tower 106 the solvent is then introduced into the acidic gas concentrating tower 104 as the solvent used in the acidic gas absorption tower 101 a solvent of physical absorption such as a mixture solution of diethyl ether and a polyethylene glycols can be used also the temperature of the crude gas in the acidic gas absorption tower 101 is preferably 20 u00b0 c to 40 u00b0 c the acidic gas concentrating tower 104 strips by flash h 2 co co 2 or the like dissolved in the solvent h 2 co co 2 or the like stripped in the acidic gas concentrating tower 104 can be introduced again into the acidic gas absorption tower 101 through a compressor 105 d the solvent is.