A radar device includes: a housing that includes an aperture in a front direction as a transmitting direction of an electromagnetic wave; a circuit board disposed in the housing such that a board surface extends along the front direction; an antenna unit that includes antenna elements being arrayed along a direction intersecting the front direction in a region on a side in the front direction of the circuit board, and that transmits the electromagnetic wave to the outside of the housing through the aperture and receives a reflected wave of the electromagnetic wave; and a dielectric lens that is disposed in the aperture of the housing to extend along a direction in which the antenna elements are arrayed and that has a semi-cylindrical shape or a parabolic-cylindrical shape projecting in the front direction.