A slot antenna comprising a dielectric substrate, a high-frequency signal transmission line formed on one surface of said dielectric substrate and having an open end, and a ground layer formed on the other surface of said dielectric substrate, said ground layer having a slot at a position opposed to the open end of said transmission line, wherein a dielectric plate for impedance matching is laminated on the surface of said ground layer on the side where said slot is formed so as to cover said slot. The slot antenna not only features a high antenna efficiency but also can be easily and cheaply produced by a layer-laminating method which is a generally employed technology for producing multi-layer wiring substrates. Besides, the slot antenna has a very simple structure which is small in size and is light in weight, and can be very well adapted to the systems that require these characteristics.