This invention consists in a locking device for the reversing gear of combustion engines, with one reversing shaft and one or more auxiliary shafts for setting the valve gear to starting, working or stop, characterised by one or more locking elements connected to the reversing shaft, and one or more recesses provided on the auxiliary shafts, co-operating in such a manner that the reversing shaft can be turned within the reversing range only when the auxiliary shaft is in the stop position, and conversely that the auxiliary shaft can be moved from the stop position only when the reversing shaft is not in a position within the reversing range.,