To simplify the configuration, facilitate execution of works at the site, and give a fine appearance by setting a ridge body between a left and a right ridge underlay material which are fixed to the left and the right side of a ventilating opening, and forming a ventilation passage in the ridge part.

A left and a right ridge underlay material 20 are secured to the upper side faces of a roof member R on the left and right of a ventilating opening H opened in the roof member R, and a ridge body 1 is installed fast over the opening H through an upper and a lower assembly block 30, 40 fixed to the underlays 20. The ridge body 1 is divided into a ridge body upper part 3 in the central part supported fast by the upper and lower blocks 30, 40 located at the upper and lower edges of the underlays 20 and a left and a right body lower part 6 supported fast by the lower block 40 arranged at the lower edges of the underlays 20. The gap between the lower edge of the ridge body part 3 and the upper edge of the ridge body lower part 6 is led to the outside so as to serve as a roof vent 9, which is put in communication with the opening H, and a water gradient is set in the part of underlays 20 situated right under the roof ventilating opening 9.