A method for measuring a deformation of a surface of an object on the basis of a two-dimensional grid image of the surface of the object reflected on pixels on an imaging surface of a camera, wherein the two-dimensional grid image of the surface of the object before the deformation is taken by the camera in such a state that the directions i and j of the camera pixels are adjusted to those, x and y, of the two-dimensional grid image, and one period of the two-dimensional grid image is adjusted in the x direction to Nx pixels of the imaging surface aligned along the i-direction and in the y direction to Ny pixels thereof aligned along the j-direction, where Nx and Ny are integers greater than 2, the method comprising the steps of: 1) taking an image of the two-dimensional grid on the surface of the object before the deformation by the camera, 2) cutting a pixel region including Nx × Ny pixels corresponding to one period of the grid image in the x and y directions out from the two-dimensional grid image reflected on the imaging surface, and carrying out a two-dimensional Fourier transformation, 3) sampling the components of the frequencies (1, 0) or (-1, 0) and (0, 1) or (0, -1) in a Fourier transform plane obtained from the two-dimensional Fourier transformation, 4) finding phases of the sampled frequencies from either set of components in the x and the y directions, and relating thus found phases with a pixel of the cut out pixel region, and storing the phases as data, 5) carrying out the above-described processes 2), 3) and 4) for all pixels by shifting the cut-out pixel region by one pixel and carrying out the two-dimensional Fourier transformation successively to relate every pixel with the two pieces of data and storing them as phase distributions, 6) phase unwrapping the thus-gained phase distributions in the x and the y directions respectively to obtain the phase distributions in the x and the y directions on the entire surface of the object, 7) multiplying the phase in the x direction by p/ and that in the y direction by q/ to convert the phase distributions to location distributions, wherein p and q are periods of the grid in the x direction and the y direction, respectively, 8) carrying out the above-described processes through on the surface of the object after deformation to obtain the grid location distribution, and acquire the deformation of the surface of the object from the difference in the grid location distributions before and after the deformation. 1) taking an image of the two-dimensional grid on the surface of the object before the deformation by the camera, 2) cutting a pixel region including Nx × Ny pixels corresponding to one period of the grid image in the x and y directions out from the two-dimensional grid image reflected on the imaging surface, and carrying out a two-dimensional Fourier transformation, 3) sampling the components of the frequencies (1, 0) or (-1, 0) and (0, 1) or (0, -1) in a Fourier transform plane obtained from the two-dimensional Fourier transformation, 4) finding phases of the sampled frequencies from either set of components in the x and the y directions, and relating thus found phases with a pixel of the cut out pixel region, and storing the phases as data, 5) carrying out the above-described processes 2), 3) and 4) for all pixels by shifting the cut-out pixel region by one pixel and carrying out the two-dimensional Fourier transformation successively to relate every pixel with the two pieces of data and storing them as phase distributions, 6) phase unwrapping the thus-gained phase distributions in the x and the y directions respectively to obtain the phase distributions in the x and the y directions on the entire surface of the object, 7) multiplying the phase in the x direction by p/ and that in the y direction by q/ to convert the phase distributions to location distributions, wherein p and q are periods of the grid in the x direction and the y direction, respectively, 8) carrying out the above-described processes through on the surface of the object after deformation to obtain the grid location distribution, and acquire the deformation of the surface of the object from the difference in the grid location distributions before and after the deformation.