A gas clean-up unit, comprising: a first conversion unit configured to perform a first conversion process of converting hydrogen cyanide contained in coal gasification gas to ammonia, and converting carbonyl sulfide contained therein to hydrogen sulfide in presence of a first catalyst and at a first predetermined temperature of equal to or higher than 240 degrees Celsius and equal to or lower than 350 degrees Celsius; a second conversion unit configured to perform a second conversion process of converting carbonyl sulfide remained in the gas coal gasification gas that has been subjected to the first conversion process to hydrogen sulfide, in presence of a second catalyst and at a second predetermined temperature of equal to or higher than 150 degrees Celsius and equal to or lower than 240 degrees Celsius; a cleaning unit (13,15) configured to perform a cleaning process of bringing the coal gasification gas into gas-liquid contact with cleaning liquid to remove ammonia, halogen and hydrocarbon traces by cleaning; and a desulfurization unit configured to absorb and remove hydrogen sulfide in the coal gasification gas by bringing the coal gasification gas that has been subjected to the cleaning process into gas-liquid contact with absorbent, wherein the cleaning unit includes a first cleaning unit configured to perform a first cleaning process of bringing the coal gasification gas that has been subjected to the first conversion process into gas-liquid contact with cleaning liquid, and a second cleaning unit configured to perform a second cleaning process of bringing the coal gasification gas that has been subjected to the second conversion process into gas-liquid contact with cleaning liquid. a first conversion unit configured to perform a first conversion process of converting hydrogen cyanide contained in coal gasification gas to ammonia, and converting carbonyl sulfide contained therein to hydrogen sulfide in presence of a first catalyst and at a first predetermined temperature of equal to or higher than 240 degrees Celsius and equal to or lower than 350 degrees Celsius; a second conversion unit configured to perform a second conversion process of converting carbonyl sulfide remained in the gas coal gasification gas that has been subjected to the first conversion process to hydrogen sulfide, in presence of a second catalyst and at a second predetermined temperature of equal to or higher than 150 degrees Celsius and equal to or lower than 240 degrees Celsius; a cleaning unit (13,15) configured to perform a cleaning process of bringing the coal gasification gas into gas-liquid contact with cleaning liquid to remove ammonia, halogen and hydrocarbon traces by cleaning; and a desulfurization unit configured to absorb and remove hydrogen sulfide in the coal gasification gas by bringing the coal gasification gas that has been subjected to the cleaning process into gas-liquid contact with absorbent, wherein the cleaning unit includes a first cleaning unit configured to perform a first cleaning process of bringing the coal gasification gas that has been subjected to the first conversion process into gas-liquid contact with cleaning liquid, and a second cleaning unit configured to perform a second cleaning process of bringing the coal gasification gas that has been subjected to the second conversion process into gas-liquid contact with cleaning liquid.