A radar device includes: a case having an opening at the front in a forward direction, which is a transmission direction of electromagnetic waves; a circuit board placed in the case, the circuit board having first and second circuit board parts, one component side of the first circuit board part facing in the forward direction, the component sides of the second circuit board part extending along the forward direction; a transmission antenna and reception antenna composed of a plurality of antenna elements placed into an array in a direction crossing the forward direction in an area, facing in the forward direction, on the circuit board; and a dielectric lens having a semi-cylindrical or parabolic cylindrical shape in the forward direction, the dielectric lens being placed in the opening in the case so as to extend along a direction in which the plurality of antenna elements are placed into an array.