Current autofocus technique in the microscope lacks speed, and it takes about one second to focus on the object. It was a bottleneck of the speed-up of the microscope measurement. To solve this problem, we have proposed "depth from diffraction" method that can estimate depth of cells under microscope from their diffraction pattern. In this paper, we propose a new algolism to estimate the depth position of cells with wider range using "Depth From Diffraction", and validated its effectiveness from autofocusing experiment.