In a multi-deck-elevator-equipped building control system, operating modes of an elevator control portion include a double operating mode. In the double operating mode, only a first cage is permitted to stop at first cage stop floors, and only a second cage is permitted to stop at second cage stop floors that are distinct from the first cage stop floors. A building fixture control portion has a first group control portion for associatively controlling an electrical fixture on the first cage stop floors and a second group control portion for associatively controlling an electrical fixture on the second cage stop floors.