This paper proposes a method of estimating multiview camera parameters for cases in which the structure of objects is unknown. The proposed method uses multiple rectangles in the 2-D images captured with the same focal length as the keys to estimate camera parameters. In this method, the 3-D coordinates of rectangles are first estimated from all images by using the characteristic of rectangles and the least squares method. Then, all camera parameters are estimated by using the estimated 3-D coordinates of rectangles and the least squares method. Finally, all parameters, that is, 3-D coordinates of rectangles and camera parameters, are corrected to minimize the errors in all images. Experimental results show that the proposed method gives good estimations of the multiview camera parameters required to obtain ray information for cases in which the shape of objects is unknown. This means that ray information can be acquired by using one ordinary camera instead of a special camera controlled by computer.