Abstract: A locking device for a bicycle or a corresponding lockable unit, which comprises a locking member swingable from a releasing position through a wheel of the lockable unit to a locking position and vice versa. A catch is provided to receive the free end of the locking member and a cylinder lock is attached to the other end of the locking member; and, in order to move the free end of the locking member into the catch and to remove it therefrom, the locking member has to be turned around a longitudinal axis. The swinging movement of the locking member between its locking and releasing positions is dependent on the turning position of the locking member so that the swinging movement can be carried out only when the locking member is in a certain turning position.