To provide an ventilating device of an air conditioner, easy to design, excellent in workability, and good in terms of its cost, since a ventilating unit formed as a separate member in the indoor unit of the air conditioner can be added without increasing the occupied area of a wall.

In this ventilating device 20 of the air conditioner, a blower casing 21 equipped with a blower 22 in an air passage connecting an ventilating opening 23 provided in the front and/or around it and a ventilation port 24 provided in the back is disposed between the indoor unit 10 and the wall surface 30 of the air conditioner.