To provide an installation structure of a central ventilation apparatus allowing easily installing of a ventilation unit body and easily performing piping even when providing a containing chamber between an upper floor and a lower floor.

The ventilation unit body 11 is placed in the containing chamber 3 between the upper floor and the lower floor, and the indoor supply pipes 13, 14 connected to the ventilation unit body 11 are extended to the sides of the containing chamber 3 with being arranged on both upper part side and lower part side of the containing chamber 3. Thereby, the indoor supply pipes 13, 14 can be efficiently piped using the level of the containing chamber 3 and piping of the indoor supply pipes 13, 14 can be easily performed.