An array antenna apparatus includes a transmission-array-antenna including transmission-antenna-elements, a transmission-side
directivity control unit controlling a
directivity of the transmission-array-antenna by controlling phases of at least part of the transmission-antenna-elements, a reception-array-antenna including reception-antenna-elements, and a reception-side
directivity control unit controlling a directivity of the reception-array-antenna by controlling phases of the reception-antenna-elements. The array antenna apparatus has a composite transmission / reception directivity, in which the direction of a
grating lobe of one of the transmission-array-antenna and the reception-array-antenna agrees with the direction of a
null point or part of side lobes of the other of the transmission-array-antenna and the reception-array-antenna, and the direction of a
grating lobe of the other of the transmission-array-antenna and the reception-array-antenna agrees with the direction of a
null point or part of side lobes of the one of the transmission-array-antenna and the reception-array-antenna, and scans in a scanning range with the composite transmission / reception directivity.