A surface machining method for obtaining a planar material of a uniform thickness is provided. This method includes mounting a planar material on a surface plate, setting the coordinate axis in the plane direction of the planar material to X, Y, and setting the coordinate axis in the height direction to Z, virtualizing an XY plane including an origin of the Z direction measured as a distance Z(m,n) from the coordinates (Xm, Yn) of a virtual plane ABCD to the plate thickness center plane S composed of midpoints of segments connecting an upper surface and a lower surface of the planar material, measuring the distance in the Z direction of the plate thickness center plane from the origin in an arbitrary XY plane position, and tilting and cutting the planar material so that the difference between maximum and minimum value of the obtained height data will be minimum.