A device for locking two building boards connected to one another in a direction (V) perpendicular to a visible side. The device includes a first building board with a lateral edge (I) and a first groove and running parallel to the visible side. The device further includes at least one second building board with a lateral edge (II) and with a second groove and running parallel to the visible side, and a locking element that is placed in the first groove of the first building board to engage in the second groove of the second building board, when both grooves have reached an overlapping position after the connection of the building boards by a vertical lowering movement.