PURPOSE: To easily form joints at jointing spots, by applying an adhesives on the surface of a base member and coating a jointing material with good leveling property and then sticking a resin molded plate on the base member to cure.

CONSTITUTION: A base member 4 is placed on a trestle 10 and a bank 11 made of a resin band surrounding this base member 4 is arranged. And an epoxy adhesive, 3a mixed with glass bead having 0.5mm in diameter is applied on the whole surface of the base member 4. After that, the adhesive 3a is removed over the wider width than the joint in the place corresponding to the joint to the extent that the adhesive 3a remains as a thin water proof layer where a joint cement slurry 5a having a good leveling property is charged. Next, resin molded plates 2 are pressed on specified positions in order with a joint width. And the joint cement 5a is cured until the level becomes even to cure it.