This study is conservation works trend since 1900. Objects for study are National Treasures and Treasures in Buddhism, in wooden architecture. And researched about the factor of conservation works, roof and tile, painting and dissolution conservation works cycle by dissolution, timber change ratio. The factor of conservation works is the most, roof and tile. Conservation works cycle by dissolution is 12.8 years. Painting cycle is 16.3 years. There are two concepts of conservation works, that is restoration and preservation. There are many restoration before 1960's. To 1960's the preservation to be many to 1970's many Restoration. And since the end of 1970's is Preservation. These reasons are conservation works history of object, the rule for Heritage protection, people on works, and study of architecture. history.