An antenna apparatus includes a glass plate that is fixed to a flange of a vehicle body at a window opening portion of the vehicle body; a dielectric material; a conductive film provided between the glass plate and the dielectric material; and a monopolar feeding portion provided on the dielectric material at a surface opposite to a glass plate side and at a position capable of being capacitively coupled to the conductive film, the antenna apparatus being configured such that a clearance between an end portion of the flange of the vehicle body and an outer edge of the conductive film functions as a slot antenna, the conductive film being provided with a notch having one end as an open end at the outer edge of the conductive film in the vicinity of the feeding portion.