A radar device for a mobile body, such as a vehicle, having a high degree of installation freedom. The radar device comprises a sensor body transmitting and receiving electromagnetic waves, and path changing means placed in an electromagnetic wave path through which the electromagnetic waves pass and changing the propagation direction of the electromagnetic waves by refraction and/or reflection. Even when the installation site of the sensor body is restricted by requirements on a mobile body on which this radar device is to be mounted, the sensor body can be installed at the restricted site by changing the propagation direction of electromagnetic waves appropriately, while maintaining the functions of the sensor body appropriately.