A barrier levelling tool intended to be attached to median barrier forming continuous casting machines which provides a reinforced chute-like extension bridging the cast barrier and trailing the casting machine and which is adjustable from the face of the barrier casting machine so as to gauge and screed the flow of concrete in a smooth manner and in elimination of unsightly dips and peaks and so as to provide a constantly level top surface fully screeded and complete as it leaves the trailing chute. The present invention is a barrier levelling attachment for levelling continuously cast barriers and which trails behind the extruder head or gate of the casting machine and confines and levels the crown or upper surfaces of the barrier in avoidance of previously experienced sudden dips and peaks and in unlevel upper surfaces. The structure is adjustable and is sufficiently rigidified as to provide a supplemental screeding and finish trowelling effect on the concrete barriers as they are continuously cast.