The present invention relates to a novel shorted patch antenna device that a thickness of a conductor of an antenna, a location of a feeding point and a shape of an antenna element is easily adjustable and can be miniaturized, as well as a method therefor. The shorted patch antenna device includes: an antenna element that is composed of a folded single conductor plate and has a radiation conductor plane (2) formed on one of opposing planes of the conductor plate and a ground conductor plane (3) formed on the other plane of the opposing planes; a miniaturization section that is composed of a hole (5) formed on the ground conductor plane (3) and a slit (7) cut out from a side of the radiation conductor plane (2) or a matching adjustment plane (31) formed by bending a tip portion of the radiation conductor plane (2) toward the ground conductor plane (3); a coaxial line (8) whose inner conductor (9) extending through the hole (5) to the radiation conductor plane (2) is electrically connected to the radiation conductor plane (2) and whose external conductor (10) is grounded to the ground conductor plane (3); and a resin (16) that fills between the radiation conductor plane (2) and the ground conductor plane (3) of the antenna element.