To provide a ventilation structure of a building capable of achieving natural ventilation effectively without installing special facility or the like even if the building has a structure allowing no formation of a space such as an open ceiling or the like.

In this building including a low ceiling room and a high ceiling room having a higher ceiling than that of the low ceiling room which are arranged while being mutually adjacent across a wall, an outside outlet of air communicating with the outside is provided in the low ceiling room, an indoor vent hole communicating with the high ceiling room is provided on a wall surface near the ceiling, and the ceiling of the low ceiling room is inclined upward toward the indoor vent hole.