The antenna unit 100 includes a first antenna 10 positioned so as to face in the direction of gravity when the unit is oriented transversely, and a second antenna 20 positioned so as to face in the direction of gravity when the unit is oriented longitudinally. Based on the output of a sensor 50 that detects whether the antenna unit 100 is oriented transversely or oriented longitudinally, a switch controller 42 performs switching of an RF switch 30 so that the first antenna is used for reception or transmission of vertically polarized waves when the antenna unit 100 is oriented transversely, and the second antenna is used for reception or transmission of vertically polarized waves when the antenna unit 100 is oriented longitudinally.