A radar apparatus has a transmission array antenna for radiating electromagnetic waves containing a main lobe and a grating lobe in a transmission directivity, a reception array antenna for receiving electromagnetic waves radiated from the transmission array antenna and reflected from a target, and a microcomputer for setting the reception antenna in reception directivities one after another by placing a null point in a grating lobe receiving area of each directivity and placing the null points of the directivities at different positions. The microcomputer produces a reception signal, produced from the received electromagnetic waves containing the main lobe reflected from the target, every change of the reception directivity and detects the target from the average of the reception signals.