Provided is an in-vehicle radar device and a cover for the in-vehicle radar device which are capable of accurately detecting an object.The in-vehicle radar device radiates electromagnetic waves and receives reflected waves, from the object, of the electromagnetic waves so as to detect a location of the object, and includes: 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 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, and the cover member includes: a cover portion that covers the transmission-and-reception surface; and a lower protrusion portion that is provided below the cover portion and formed so as to protrude on a surface side of the cover member with respect to the cover portion, the cover portion being formed of a material through which the electromagnetic waves are transmitted.