Disclosed is a method of detecting relative positional deviation of a first object with a first grating pattern having an optical power and a second object with a second grating mark having an optical power. Light diffracted by both the first and second grating marks forms a light pattern on a predetermined plane; wherein different diffraction beams of the light diffracted by both the first and second grating marks are displaceable along the predetermined plane in accordance with the relative positional deviation of the first and second objects, in the same direction and by substantially the same quantity; and the relative positional deviation of the first and second objects is detected on the basis of the position of the light pattern on the predetermined plane.