To withstand an earthquake and a storm and reduce cost by securely forcing a ridge hardware to pierce a sheathing roof board and reach a rafter and then fitting a pentagonal under-ridge wood matched with a ridge metal plate.

After sheating roof boards are laid, a ridge hardware 3 is securely fixed to rafters 8 from above the sheating roof boards. A pentagonal under- ridge wood matched with the top angle of the ridge metal plate 1 is fixed to the ridge hardware 3 with screws or nails. Roof tiles 5 are laid and a waterproof packing 4 is attached and then, the ridge metal plate 1 is fitted to the under-ridge wood 2. The top of the ridge metal plate can be arcuately shaped by arcuately shaping the top of the under-ridge wood. In this way, since the sheathing roof boads can be securely fixed to the rafters, the building can withstands an earthquake and a storm and it is not necesarry to make holes in the hard roof tile and hence, a drill edge does not wear and labor cost can be reduced and further, the ridge hardware can be fixedly fitted and the cost can be reduced. Moreover, an arcuate ridge metal plate can be used.