A detector detects head postures and gaze directions from images of a person to be measured captured by an imaging unit; a generation unit generates a gaze direction distribution with respect to each of the head postures, from the head postures and the gaze directions detected by the detector; a calibration unit determines predetermined one of the head postures as a reference posture, and calculates calibration parameters to be used to calibrate the gaze direction distribution with respect to the reference posture; and a correction unit corrects the gaze direction distributions with respect to the head postures other than the reference posture by using the calibration parameters calculated by the calibration unit. This reduces the influence on the calibration which may vary due to change in the head posture.