To provide a decentration measuring method or the like capable of measuring a decentration amount always highly accurately, regardless of a shape error of the surface to be inspected.

This method has a first reference object position measuring process for measuring positions of three balls 100d or the like provided on a lens frame 100c; an optical element shape measuring process for measuring the shape of a prescribed surface of a lens 100; a measuring coordinate system calculation process for calculating the position of a measuring coordinate system relative to the lens frame 100c; a coordinate conversion calculation process for performing coordinate conversion of a measurement result in the optical element shape measuring process into the measuring coordinate system; a support process for supporting the lens frame 100c by a fixing frame 140 (mounting part 160); a second reference object position measuring process for measuring the position of the ball 100d of the supported lens frame 100c; a first frame body decentration amount calculation process for calculating the decentration amount to a reference axis 160a of the lens frame 100c; and an optical element decentration amount calculation process for calculating the decentration amount of the lens 100 to the reference axis 160a.