To supply the dried compressed air to the consumption side by comprising a refrigerating-type air dryer on a dehumidifier for cooling and drying the compressed air to be supplied from a receiver tank to the consumption side, and providing this refrigerating-type air dryer with a refrigerating compressor driven by an engine.

The compressed air compressed by an air compressor body 4 driven by an engine 3 is stored in a receiver tank 5 through a conduit with the lubricating oil for lubricating.sealing.cooling a compression chamber of the air compressor body 4. Then the compressed air and the lubricating oil are separated by a separator, and the separated compressed air is sent to an after-cooling 11 to be cooled by the cooling air flow sucked into a noise insulation box 2 by a cooling fan 8. Whereby the water vapour in the compressed air is condensed, and only the compressed air is introduced into an evaporator 13 of the refrigerating-type air dryer. The compressed air introduced into the evaporator 13 is cooled in the evaporator, the water vapour in the compressed air is condensed, and the compressed air is discharged to the consumption side.