The invention relates to laser devices for constructing planes, in particular to laser levelling instruments. Known are laser levelling instruments with a self-levelling support plate on which are placed laser radiation sources, prisms for unrolling planes from the laser beams and a laser plummet, a power supply with control and a holder for attachment to a stand, wherein the optical axis of the laser plummet extends over the centre of the holder. In order to increase in such laser levelling instruments the useful properties and to expand the functionalities, the laser radiation sources and the prisms for unrolling planes from the laser beams are combined into at least one radiation module. Furthermore, the radiation module is provided with a housing, in which additionally the following are mounted: an apparatus for horizontal fine-adjustment, an additional power supply with a control, an additional self-levelling support plate for receiving the laser radiation sources and the prisms for unrolling the plane from laser beams. Furthermore, the laser plummet with the self-levelling support plate, the power supply with control and the holder for attachment to the stand are combined into a holder module which is provided with a housing. Finally, the housing of the at least one radiation module and the housing of the holder module are configured such that the radiation module can be coupled to the holder module and the connection of at least one additional radiation module is possible.