Transmission assembly with a lock gate structure for an optical disc device for preventing pieces of an optical disc from escaping the optical disc device

An optical disc device includes a budging mechanism, a transmission assembly, a disc holding down plate, and a lock gate structure. The budging mechanism is moved by mechanically interfering with the optical disc entering the working area of the optical disc device to drive the transmission assembly mounted on one side of the optical device so as to further operate the disc holding down plate and the lock gate structure. In such mechanical connections, the working timing of all the device and mechanisms can be controlled so as to drive the lock gate to open or close the loading slot in the right time.