A compressed air drier includes a support base, a desiccant cartridge coupled to the support base, and a case that covers the cartridge and is coupled to the support base. The support base includes an inlet for compressed air from a compressor, an outlet for the compressed air, and a discharge port for oil and water including a drain valve device. An electrically charged oil adsorbent is accommodated between the cartridge and the case. The cartridge is filled with a desiccant. The compressed air drier dries the compressed air entering the inlet with the desiccant during a loading operation, collects the dried compressed air in the case, and discharges the dried compressed air from the outlet. The compressed air drier passes the compressed air in the case through the cartridge during an unloading operation to discharge oil and water from the discharge port.