Abstract: The present invention relates to an air liquefaction separation apparatus whose power cost is reduced. A low-pressure column of a double rectification column has a cleaning section at a lower position, and a liquid oxygen is partly withdrawn from the space above the cleaning section so as to supply it to a main condenser-evaporator. The liquid oxygen supplied to the main condenser-evaporator is subjected to heat exchange with a nitrogen gas separated at the head of a high-pressure column to be gasified into an oxygen gas. This oxygen gas is introduced to the space under the cleaning section. Hydrocarbons contained in the oxygen gas ascending through the cleaning section are removed by the rest of the liquid oxygen descending through the cleaning section to provide a clean oxygen gas. The liquid oxygen passed through the cleaning section is withdrawn from the low-pressure column.