A fixing device of an antenna device includes a base member, a fixing member, a bolt and a guide which guides the base member to a fixing opening. The fixing device takes a main fixed state in which the mounting surface is clamped between the fixing member and the base member after inserting the fixing member into the fixing opening and rotating the fixing member at a predetermined angle, and an initial fixed state in which the fixing device is fixed before the fixing member is rotated at the predetermined angle. The guide is arranged at a position to surround the fixing member in the initial fixed state, and includes guide portions which have greater height than that of a lower end of the fixing member in the initial fixed state.
