PURPOSE: To provide an air liquefaction and separation method and device capable of pre-cooling raw material air down to a predetermined temperature without using any fluorocarbon freezer.

CONSTITUTION: In the case that raw material air compressed by a compressor 1 to increase its temperature is cooled down to an operating temperature of an adsorbing device 7, the raw material gas is fed into a precooling heat exchanger 3 and heat exchanged with low temperature gas such as product nitrogen gas GN or discharged gas WG of the like fed out of a main heat exchanger 8.