An actuator (1) having two detent devices (2) which include in each case at least one terminal detent element (3) for a part (27) of a drive train, and at least one adjustment element (4, 19) which is operatively connected to the terminal detent element (3) and is specified for setting a position of the terminal detent element (3). The at least one gear unit (5, 18) is disposed between the at least one terminal detent element (3) and the at least one adjustment element (4, 19).