An in-vehicle radar device which radiates electromagnetic waves and receives reflected waves, from an object, of the electromagnetic waves so as to detect a location of the object and which is mounted on a rear of a vehicle, the in-vehicle radar device including: a transmission-and-reception section that transmits the electromagnetic waves and receives the reflected waves; a detection section that detects the location of the object based on the reflected waves; and a cover member that is provided below a rear bumper of the vehicle and that covers the transmission-and-reception section in a manner that a rear surface of the cover member faces a transmission-and-reception surface of the transmission-and-reception section so as to be spaced apart therefrom.