A compressed-air drying system configured to remove oil and water contained in compressed air delivered from a compressor, the system comprising: a compressor; an air dryer including desiccant and a drain port configured to drain liquid generated through regeneration of the desiccant; an oil mist separator (11, 11A, 11B) that includes a trapping portion configured to trap oil contained, as oil mist, in the compressed air, and a drain port configured to drain liquid containing the trapped oil, wherein the oil mist separator (11, 11A, 11B) is provided in a passage between the compressor and the air dryer; and a reservoir configured to store the liquid drained from the air dryer and the liquid drained from the oil mist separator (11, 11A, 11B), wherein the drain port of the air dryer and the drain port of the oil mist separator (11, 11A, 11B) are connected to the reservoir wherein the compressed-air drying system further comprises a drain passage (32, 43) configured to drain, to the reservoir, the liquid drained from the air dryer and the liquid drained from the oil mist separator (11, 11A, 11B); and a connecting portion (30, 42) that connects, to the drain passage (32, 43), the drain port of the air dryer and the drain port of the oil mist separator (11, 11A, 11B) wherein the drain port of the air dryer is connected to an upstream drain passage configured to drain the liquid drained from the air dryer to a downstream side, and wherein the connecting portion is T-shaped and includes a first inlet, a second inlet connected to the upstream drain passage, and an outlet connected to the drain passage, characterized in that, the first inlet of the connecting portion is directly connected to the drain port of the oil mist separator (11, 11A, 11B) and in that the first inlet and the outlet of the connecting portion are connected to each other by a straight passage (33, 35, 36). a compressor; an air dryer including desiccant and a drain port configured to drain liquid generated through regeneration of the desiccant; an oil mist separator (11, 11A, 11B) that includes a trapping portion configured to trap oil contained, as oil mist, in the compressed air, and a drain port configured to drain liquid containing the trapped oil, wherein the oil mist separator (11, 11A, 11B) is provided in a passage between the compressor and the air dryer; and a trapping portion configured to trap oil contained, as oil mist, in the compressed air, and a drain port configured to drain liquid containing the trapped oil, wherein the oil mist separator (11, 11A, 11B) is provided in a passage between the compressor and the air dryer; and a reservoir configured to store the liquid drained from the air dryer and the liquid drained from the oil mist separator (11, 11A, 11B), wherein the drain port of the air dryer and the drain port of the oil mist separator (11, 11A, 11B) are connected to the reservoir wherein the compressed-air drying system further comprises a drain passage (32, 43) configured to drain, to the reservoir, the liquid drained from the air dryer and the liquid drained from the oil mist separator (11, 11A, 11B); and a connecting portion (30, 42) that connects, to the drain passage (32, 43), the drain port of the air dryer and the drain port of the oil mist separator (11, 11A, 11B) wherein the drain port of the air dryer is connected to an upstream drain passage configured to drain the liquid drained from the air dryer to a downstream side, and wherein the connecting portion is T-shaped and includes a first inlet, a second inlet connected to the upstream drain passage, and an outlet connected to the drain passage, characterized in that, the first inlet of the connecting portion is directly connected to the drain port of the oil mist separator (11, 11A, 11B) and in that the first inlet and the outlet of the connecting portion are connected to each other by a straight passage (33, 35, 36). a first inlet, a second inlet connected to the upstream drain passage, and an outlet connected to the drain passage, characterized in that, the first inlet of the connecting portion is directly connected to the drain port of the oil mist separator (11, 11A, 11B) and in that the first inlet and the outlet of the connecting portion are connected to each other by a straight passage (33, 35, 36).