Later, to expand the capacity for the Japan World Exposition '70 held in 1970, a new high-rise building was planned to be built at the south of the dining room of the main building, but because the area was under several regulations as for scenic reserve, it was called off when the basic foundation was completed of which a modern half-underground grillroom has been newly built on the base; in accordance with it, the unnecessary lounge was removed.
その後、1970年に開催された日本万国博覧会に備えて収容力の拡大を図るべく、本館食堂の南側に高層ビル形態の新館建設を計画し、基礎工事まで済ませたが、景観保護にかかる諸条例の規制区域であったため、これは中止となり、その基礎を生かして近代的な外観の半地下式グリルが新設され、これに伴い不要となったラウンジが撤去されるに留まった。