A conductor pattern of an antenna device is provided in a notch and includes a common conductor, a first conductor, and a second conductor. A power supply unit is disposed at a connection portion between a conductor plate and the conductor pattern. Each of the first conductor and the second conductor is connected to the power supply unit with the common conductor interposed therebetween. The power supply unit is positioned at a position at which a distance to an opening end is shorter than a distance to a closed end at a side end. A first partial conductor of the first conductor is positioned between the second conductor and a side end. A length of the first conductor in a direction along the side end is longer than a length of the second conductor in the direction along the side end.