A starting device for an automatic transmission for a vehicle includes a hydraulic coupling disposed between the output shaft of the engine and the input shaft of the automatic transmission. A lock-up clutch connects the output shafts of the engine and the output side of the hydraulic coupling, the output side of the hydraulic coupling being connected to the input shaft of the automatic transmission. A slip clutch is connected in series with the lock-up clutch, is disposed between the output shaft of the engine and the output side of the hydraulic coupling, and includes a plurality of friction plates and a biasing device for applying a predetermined biasing force to the plurality of friction plates to urge the friction plates together. Additionally, a cam mechanism is disposed in the power transmission path with the slip clutch at the output side of the hydraulic coupling, for generating an axial force proportional to the amount of torque transmitted through the power transmission path and for applying the torque to the plurality of friction plates of the slip clutch so that the slip clutch has a torque capacity proportional to the applied torque.