for by a cross support 3 by way of links 4 rotatably joined with support bar 3 and having turnpins 5 and 6 at their ends for joining them with straight edges 1 and 2 so that turning motion of the links in relation to the straight edges 1 and 2 is made possible the two headed arrows to be seen in fig1 are to make it clear that the straight edges may be moved backwards and forwards lengthways part of the apparatus with the straight edges is joined with a support frame 7 whose forwardly running shafts 7 39 are supported by track laying units 8 of a track laying vehicle the way in which each shaft is joined with frame 7 will later be made clear in connection with fig4 in more detail there is furthermore a driving motor 9 and a box 15 with controls therefor straight edges 1 and 2 are marked in dash lines the shafts 7 39 are guided by guides 14 on the two track laying units fig2 is a view of the apparatus looking towards the straight edges and placed on a covering 12 which is to be leveled and screeded it is possible to see the links 4 placed over and joined turningly with straight edges 1 and 2 furthermore there is an adjustment system 10 of which more details will be given later in connection with fig4 fig3 39 and 3 34 are side views of the apparatus the frame 7 and the near side track laying unit 8 together with the driving motor 9 and the box 15 with controls straight edges.