To improve inspection accuracy and reduce inspection time with a small number of data in a warp inspection of an optical disk.

A camming (displacement in an axial direction) and a warp angle of an optical disk 1 are measured with rotating the optical disk 1 by an optical detector 10 placed at a few radius positions fixed in the optical disk 1. By interpolation processing fitting measuring data to a curve by the optical detector 10 using an analytic solution satisfying a bending equation for a thin disc, which is a relatively simple numerical expression on a warp phenomenon, the camming and warp angle data of a whole optical disc are obtained and the warp inspection is performed. Also, the result of the interpolation processing is recorded as the coefficient of the interpolation equation.