The purpose of the present invention is to enable a secure attachment of an antenna element and to facilitate adjustment of the antenna element characteristics. Rearward of a spoiler are formed a plurality of lateral grooves extending in a left-right direction of a vehicle, and a plurality of vertical grooves extending in a front-rear direction of the vehicle. The plurality of lateral grooves and the plurality of vertical grooves form latticed grooves as grooves in the shape of a lattice for installing an antenna element. The antenna element is formed by a conductive wire. One end of the antenna element is connected to an amplifier, and the other end is opened. The antenna element extends from the amplifier via a power feeding groove and the right-end one of the vertical grooves to the rear end of the groove, from which the antenna element is fitted in a route along the most rearward one of the lateral grooves to the vicinity of the left-end one of the vertical grooves, thus being securely attached to the spoiler.