To provide a technology of a structure of a drying container in a compressed air drying apparatus for preventing abnormal noise and impact due to the up and down vibrations of a purge tank following load operation and unload operation of the compressed air drying apparatus.

One or a plurality of projected parts 16m for back-flow member installation are expansively formed in the upper end rim of a drying container 16 and a small continuous through-hole 16n communicated with a first room 17a of a purge tank 17 for storing compressed air is formed in the lower face and a back-flow member housing hole 22E communicated with the hole is formed. A compressed air back-flow member 22 is composed of a push nut 22A, a valve stopper 22B, a valve spring 22C, and a spherical body 22D and is housed in the back-flow member housing hole 22E. The bottom face of the back-flow member housing hole 22E forms a mortar-like recessed part 22F and is enabled to set the spherical body 22D in a freely movable manner.