A compressed-air drying system includes an air dryer, an oil mist separator and a reservoir. The air dryer includes desiccant and a drain port for draining liquid generated through regeneration of the desiccant. The oil mist separator includes a trapping portion for trapping oil contained, as oil mist, in the compressed air. The oil mist separator further includes a drain port for draining liquid containing the trapped oil. The oil mist separator is provided in a passage between the compressor and the air dryer. The reservoir stores the liquid drained from the air dryer and the liquid drained from the oil mist separator. The drain port of the air dryer and the drain port of the oil mist separator are connected to the reservoir.