A calibration device acquires an image of an imaging target located ahead of a vehicle. Images of the imaging targets behind the vehicle are acquired, which are different from the acquired images captured in the forward direction. The shape and size of the imaging targets are already known. The calibration device performs projective transformation for the imaging targets shown in overlap regions of the acquired images, and identifies a roll, a pitch and a vertical position of each camera such that the conversion results are in agreement with the shape and size of the targets. The calibration device identifies an x-coordinate, a y-coordinate, and a yaw of each camera such that one link angle in a virtual link structure is minimized.