An antenna device is designed to be connected to a printed-circuit board having a feeding part and a board ground. The antenna device includes a feed antenna, an antenna ground having a plate shape, an artificial magnetic conductor having a plate shape and being formed between the feed antenna and the antenna ground, a first connection connecting the feed antenna with the feeding part by passing through the antenna ground and the artificial magnetic conductor, and a second connection connecting the antenna ground with the board ground. The artificial magnetic conductor is not connected to the first connection and the second connection.