A patch antenna device and an antenna device that are miniaturized while avoiding degradation of radiation characteristics, such as gain and efficiency. A first electrode is formed on a front surface of a rectangular parallelepiped-shaped dielectric substrate. A second electrode is formed on a rear surface of the dielectric substrate. The first electrode is connected through a coaxial cable to a power supply unit. The width W of each of the first and second electrodes is smaller than or equal to a quarter of the length L thereof, and the thickness T of the dielectric substrate is larger than or equal to the above width W. Advantageously, the second electrode is set so as to be longer than the first electrode, and both end portions of the second electrode are bent and arranged on both end surfaces of the dielectric substrate.