PURPOSE: To improve the working efficiency by forming a reference base which has a reference curved surface on the lower side and uses the upper side as a placing surface for extension tiles and insertin an elastic body of a plate material in a space between the reference base and the upper surface of pantile.

CONSTITUTION: A reference base 2 is placed on the upper surface of a pantile 1 in such a manner that the reference curved surface of the base meets the upper surface, thereof and the upper surface of the reference base 2 is decided in its width by width deciding fittings 12. A bolt 14 erected on a ridge post 13 is inserted in a bolt hole of the width deciding fitting 12, and an elastic body 8 is inserted in a gap between the reference curved surface and the pantile 1 so as to accomplish tight connection by the bolt 14 and a nut 15. Subsequently, an extension tile fixing plate 16 is longitudinally provided on the upper surface of the reference base 2, and an extension tile 17 is fixed to the extension tile fixing plate 16 to be covered with a round tile 18. Accordingly, water tightness higher than those of ridge earth and mortar can be maintained.