A millimeter wave radar for the purpose of automatic operation or collision prevention of a vehicle which solves the problem that a side lobe of a transmitted electromagnetic wave is reflected by surrounding bodies and the reflected wave is received, with the result that unnecessary bodies may also be detected. A layer higher in dielectric loss than a radome or a magnetic loss layer and a conductor layer in a mesh form are embedded in a part of the inside surface of the radome, whereby it is possible to provide a millimeter wave radar which is light in weight, excellent in weathering performance, inexpensive, and excellent in detection performance.