To realize an antenna device that can operate in wide bands (in a plurality of frequency bands) and can achieve an excellent antenna gain and maintain non-directivity of vertically polarized waves in each band in a space-saving manner, and also to provide a technique capable of maintaining mechanical reliability of the antenna device.An antenna device including; an approximately U-shaped conductor antenna, on one end side of which a power feeding portion is provided and on the other end side of which an end portion is provided as an open end terminal, and which has a folded-back portion; a base body made of an insulating material; a substrate on which said conductor antenna and said base body are mounted; conductor planes of said one end side and said the other end side of said conductor antenna constituted to be approximately perpendicular to each other; said base body being fixed on said substrate; at least said one end side of said conductor antenna being fixed on said base body; and said folded-back portion being fixed on said substrate.