The antenna device for mobile telephony comprises an antenna mast, at least one antenna connected to the antenna mast, and means for placing the antenna on a building. The antenna device comprises fastening means to connect the antenna mast to an upright wall of a building, and a platform connected to the antenna mast above the fastening means, the antenna mast being directed approximately perpendicularly to the platform. The platform is arranged to be supported on a horizontal surface of the outside of the building without a fixed connection between the building and the platform having been effected.
