An antenna device is provided. The antenna device includes an antenna part, a motor and a case. The antenna part has a transmission antenna configured to transmit a radio wave and a reception antenna disposed on one of an upper side and a lower side of the transmission antenna and configured to receive a radio wave. The motor rotates the antenna part. The case covers the antenna part. The case has a side wall. The side wall has two inclined portions inclined at different inclination angles with respect to a rotational axis of the antenna part. A boundary between the two inclined portions is located higher than half of a height of the case.