A position-securing mechanism and a device unit equipped therewith for securing a working device to a trailer is designed to the working device is attachable to a working machine via a coupling device. The position-securing mechanism is formed with a sensor designed to detect a coupled state and a decoupled state of the coupling device, a receiving device having first and second functional sections provided on a first longitudinal side of the trailer or the working device, a locking device that is brought into a locked state in which this locking device prevents the release of the engagement of the functional sections and into an unlocked state in which this locking device permits the release of this engagement and a drive device connected to the sensor and driven thereby.