In an antenna adapted to be mounted on a vehicle body, a base member supports a base end of the antenna element. A screw member is extended from the base member and adapted to be inserted into a though hole formed in the vehicle body. A wall member is extended from the base member to define a housing space. A circuit board is disposed in the housing space. A casing covers the housing space such that an inner face thereof comes in contact with an outer face of the wall member. A waterproofing member is disposed between the base member and the vehicle body so as to surround an entire periphery of the through hole.