Ranzan Country Club is a golf clubhouse built in 1961, designed by architect Taro Amano, a student of F.L. Wright. It was selected in 2014 for the docomomo lapan 174, a selection of 174 important modern buildings complied by docomomo Japan. After completion, it underwent unplanned extension and reconstruction work a number of times. A new conservation and restoration plan began in 2010, and the project is now in the 5th stage. Following a master plan, construction work has been carried out whilst the clubhouse has continued in operation. The building is owned by a private company and has not been designated as a cultural property. The process of this conservation and restoration project serves as a leading example for similar projects in the future. In this project, the original portions of the building will be left intact while the later extensions and alterations are removed, restoring it to original state while taking operational requirements into consideration. The plan is divided into three categories: safety/regulatory issues, managerial issues, and aesthetics/comfort. Prioritization of these three issues is decided partially based on surveys of club members. As part of the restoration, studies were carried out including site surveys and detailed measurement surveys, as well as carbonation tests and destructive strength testing of concrete core samples. We also carried out interviews of the managers and documentary searches of the drawings, literature, contracts, etc. Through these preliminary studies, it was discovered that the building had undergone major extension and reconstruction works four times by 2010 losing a number of its principle elements, and that many of the surface finishes were added later to conceal wiring installed for newly-added facilities. One reason for addition of these additional finishes is that very few places were left to conceal newly-added wiring because the clubhouse structure itself composes the framework of the space. Preserving the value of the overall building and its integrity for future generations, whilst keeping it in clubhouse use, demands the addressing of multiple issues, including improving the current method of operation, upgrading the equipment system, and enhancing seismic safety.