of the base member 2 in the moving direction a together with the intervening member 11 accordingly only a small pushing force is required from the jacks 4 consequently the structure of the supporting members 5 resisting the reaction forces from the jacks 4 may be reduced in size and the entire structure for moving the precast slab 3 hence may be reduced in size with the precast slab 3 being pushed from an upstream position even if the upper surfaces 12 of the base members 2 slope upwardly from such upstream position the slabs 3 will not move in a reverse direction in another embodiment of the invention shown in fig6 a roller 14 may be installed on the lower surface 13 of the precast slab 3 to facilitate movement of the precast slab 3 together with roller 15 in the downstream direction a over the upper surface 12 of the base member 2 furthermore as shown in fig7 roller 15 may be installed on the upper surface 12 of the base member 2 and the precast slab 3 may be moved over the roller 15 roller 15 reduce the friction resistance in moving the precast slab 3 so that the precast slab 3 may be moved easily in the downstream direction a fig8 schematically illustrates a laying method of another embodiment of the invention in this embodiment multiple precast slabs 3a to 3i are placed on the base members 2 by the same procedure as in the embodiment shown in fig2 1 through fig3 such precast slabs 3a to 3i then are.