The construction of the Main Building was completed in 1968, seven years after the initial opening, thereby creating a facility that consisted of an administration building with six floors above ground and one floor underground, as well as a library building with 17 floors above ground.
本館は、開館から7年後の1968年（昭和43年）に竣工し、地上6階・地下1階の事務棟と17層の書庫棟からなる施設が完成した。