1. An imaging apparatus which has two imaging units, comprising: a correlation value calculation unit that calculates a correlation value from two images captured by the. two imaging units; a three-dimensional object detection unit that detects a three-dimensional object from the two images; a region dividing unit that divides an image region including the three-dimensional object into multiple regions; a relative speed calculation unit that calculates relative speed for every region of the multiple regions; and a reliability calculation unit that calculates reliability of the three-dimensional object, based on the relative speed calculated for every region.