GAS PURIFICATION DEVICE AND GAS PURIFICATION METHOD

To provide a gas clean-up unit and a gas purification method that can effectively reduce the concentration of carbonyl sulfide in gas to be treated even when the concentration of carbonyl sulfide in the gas to be treated is high. A gas clean-up unit 1 includes a first COS converter 12 that performs a first conversion process of converting hydrogen cyanide contained in gas to be treated Gto ammonia, in presence of a first catalyst and at a first predetermined temperature; a second COS converter 14 that performs a second conversion process of converting carbonyl sulfide in gas to be treated Gafter the first conversion process to hydrogen sulfide, in presence of a second catalyst and at a second predetermined temperature that is lower than the first predetermined temperature; a first cleaner 13 that performs a cleaning process of cleaning and removing ammonia by bringing gas to be treated Ginto gas-liquid contact with cleaning liquid; and a desulfurizer 16 that absorbs and removes hydrogen sulfide in gas to be treated Gby bringing the gas to be treated Gafter the cleaning process into gas-liquid contact with absorbent.