A measurement method for selecting a rectangle from a grid image that has been projected on a surface of an object or that has been gained by taking an image of a grid drawn on the surface of an object, inputting an image in a state where the optical system has been adjusted in such a manner that the grid phase of the above-described projected grid image or the above-described drawn grid is gained by dividing 2mπ (m is an integer) by Mx×Ny within the rectangle, sampling a rectangular region made up of Mx pixels in the x direction and Ny pixels in the y direction of the above-described grid image or an image of the above-described grid from the above-described inputted image, and finding a phase on the basis of the brightness of pixels in the above-described rectangular region.