The present invention relates to a calibration apparatus for an array antenna having a plurality of antenna elements. The calibration apparatus comprises a conversion unit detecting a calibration signal from an output of a transmission unit to convert the detected calibration signal into a predetermined reception radio frequency and outputting the converted calibration signal together with a reception main signal to a reception unit, a detecting unit detecting the calibration signal from an output of the reception unit for each of the antenna elements to obtain a relative phase difference between the calibration signals, and a phase correcting unit correcting a phase difference with respect to one of or both a transmission main signal and a reception main signal based on the obtained relative phase difference. This configuration can eliminate the need for a radio transmitter-receiver dedicated to a calibration signal, thus facilitating the calibrations.