An antenna device that can surely prevent water from coming into the part where the transmission table is introduced and allows the number of parts to be reduced so that the cost can be reduced. The antenna device includes an antenna module that receives radio waves transmitted from a satellite, a cover member having a sufficient internal space to store the antenna module and its bottom opened, and a bottom plate to close the open bottom of the cover member. The transmission cable is connected to the antenna module. The transmission cable is inserted from the hole provided at the cover member and sealed by a seal material including silicon resin in the hole. The bottom plate is made of a metal plate and a magnet plate and the magnet plate has projections to position the magnet. After the bottom plate is attached, a composite resin material is filled and the cover member has its bottom side sealed.