The invention relates to a grinding machine for grinding a workpiece, which has been set on a chuck top surface, by moving a rotating grinding wheel in relation to the workpiece. The grinding machine includes: a microscope configured to be vertically movable; a CCD camera configured to take an image viewed through the microscope; and an image processor configured to process the image taken by the CCD camera to measure a vertical distance between a reference plane of the microscope and an object of the microscope. The image processor is adapted to measure the vertical distance between the reference plane of the microscope and the object of the microscope based on sharpness of the image, which corresponds to how clear the microscope is focused.