PURPOSE: To enable the simple manufacture and easy fitting of support structure of an antenna or the like installed on the top plate of a ship cabin or the like.

CONSTITUTION: The support structure of an antenna or the like is provided with a beam 3; a pair of beam holding bodies 2 fitted to a top plate 1 so as to hold both end parts of the beam 3; flanges 4 and gromets 4 fitted to the parts where cables 10 pierce the top plate 1 so as to hold the cables 10 at the through parts by seal structure; and supporting bodies 7 fitted to the beam 3 so as to erect the antenna or the like on the beam 3. The respective beam holding bodies 2 are fitted rotatably around horizontal shafts 60, and the beam holding parts of the beam holding bodies 2 are opposed to each other regardless of the inclination of the top plate 1.