To provide an antenna device 30 capable of being easily fixed by inserting one end of a core member 10 to an insertion hole 24 of a case body 22 and obtaining sufficient strength against a force in a pull-out direction.

A hook 12 elastically deformable in a radial direction inner side with a loose end in an insertion direction is provided on one end of a cylindrical core member 10, and a roughly bar-shaped control member 32 provided with a roughly semicircular notch 32a facing the hook 12 is inserted freely rotatably around an axis inside the core member 10. A cover 16 is provided freely rotatably around the axis on the core member 10 and the control member 32 is connected to the cover 16. At the time of insertion, when the elastic deformation to the inner side of the hook 12 is allowed by the notch 32a and the engaging projection part 12a of the hook 12 is engaged and fixed to the back surface of the case body 22, the cover 16 is rotated around the axis, the control member 32 is rotated at an angle of 90 degrees and the elastic deformation to the inner side of the hook 12 is prevented at a part without the notch 32a.