A device for locking two building boards comprises a tongue element inserted into a groove a first building board. The tongue element comprises a spring having a plurality of wave arches. A groove is provided in a core of a second building board and corresponds to the groove of the first building board, such that when the groove of the first and second building boards overlap during a connection of the first and second building boards, by a vertical lowering movement, the first and second building boards are locked in a direction parallel to the visible side by the tongue element.