To provide an antenna mounting structure that enables an antenna to easily be replaced without using any special tool and eliminates the need to bore a small hole for detachment on an external surface of a housing 20.

An antenna element 32 is axially penetrated a holder member 26 and arranged movably within a designated range. A storage part 28 having an opening 28a at one end is provided on the external surface on the side of the housing 20. An elastic engagement piece 30 allows the holder member 26 to be inserted by elastic deformation when the holder member 26 is inserted into the storage part 28 on the side of the housing 20, and it elastically restores when the holder member 26 is inserted up to a designated position in the storage part 28, and is engaged with the holder member 26 and then restricts movement in a falling direction is provided on the side of the housing 20. While the antenna element 32 is drawn out, a rod type member 36 is inserted into the storage part 28 from the opening 28a to elastically deform the elastic engagement piece 30 and then the holder member 26 is disengaged from the elastic engagement piece 30 and the holder member 26 is drawn out of the storage part 28.