An antenna used in wireless communication, comprises: a dielectric substrate; a ground conductor portion arranged upon the dielectric substrate; an antenna element including a radiating conductor portion arranged upon the dielectric substrate opposite to the ground conductor portion, a shorted conductor portion that connects the radiating conductor portion and the ground conductor portion, and a power supply unit adapted to supply a high-frequency current to the radiating conductor portion; and an open conductor portion connected at high frequencies to the ground conductor portion, wherein the open conductor portion is connected to the dielectric substrate so as to protrude by a predetermined length from the location of the ground conductor portion in a diagonal direction from the location where the ground conductor portion and the shorted conductor portion are connected.