Abstract: In an automatic transmission employing a parking-lock mechanism accommodated in a transmission casing for mechanically locking and unlocking a transmission output shaft of a speed-change system, the transmission casing includes a first casing and a second casing integrally connected to each other. A shift-lever-operated manual shaft and a cam-equipped parking rod, both constructing parts of the parking-lock mechanism, are installed on the first casing, whereas a support actuator having a guide face for the cam and a pivotable parking pawl operated by the cam for meshed-engagement with a parking gear of the transmission output shaft when a specified longitudinal displacement of the parking rod has been reached, both constructing parts of the parking-lock mechanism, are installed on the second casing. A temporary-retaining structure is provided on a face of the first casing facing the second casing, for temporarily retaining the parking rod.