A device for measuring a surface distortion on a specular surface or a semi-specular surface, the device characterized by comprising: pattern displaying means capable of switching and displaying a plurality of kinds of light-and-shade patterns; capturing means for capturing mirror images, reflected in the specular or semi-specular measurement-target surface, of the plurality of light-and-shade patterns displayed on the pattern displaying means; and surface-distortion distribution calculating means adapted for performing image processing on the captured mirror images of the plurality of light-and-shade patterns to calculate surface-distortion distribution of the measurement-target surface by determining an inclination of the measurement-target surface at each point on the measurement-target surface; wherein, with x, y, z being coordinates of a point on the measurement-target surface represented by a horizontal x-y plane, X, Z being coordinates of a point on the pattern displaying means at a distance 1 in the negative y-direction, and φ being an angle relative to the y-axis, ξ being an angle relative to the z-axis and α being an elevation angle of the capturing means, the capturing means being disposed apart from the origin of the x, y, z coordinate system by a projection distance L in the positive y-direction, the inclination is determined using the equations sinφtanξ = X − 1 + M α / 2 l tanα, and cosφtanξ = Z − 1 − M z − 1 + M ytanα / 2 l 1 + tan 2 α, whereby M=1/L, sinφtanξ is the inclination of the measurement-target surface in the x-direction and cosφtanξ is the inclination of the measurement-target surface in the y-direction. pattern displaying means capable of switching and displaying a plurality of kinds of light-and-shade patterns; capturing means for capturing mirror images, reflected in the specular or semi-specular measurement-target surface, of the plurality of light-and-shade patterns displayed on the pattern displaying means; and surface-distortion distribution calculating means adapted for performing image processing on the captured mirror images of the plurality of light-and-shade patterns to calculate surface-distortion distribution of the measurement-target surface by determining an inclination of the measurement-target surface at each point on the measurement-target surface; wherein, surface-distortion distribution calculating means adapted for performing image processing on the captured mirror images of the plurality of light-and-shade patterns to calculate surface-distortion distribution of the measurement-target surface by determining an inclination of the measurement-target surface at each point on the measurement-target surface; wherein, with x, y, z being coordinates of a point on the measurement-target surface represented by a horizontal x-y plane, X, Z being coordinates of a point on the pattern displaying means at a distance 1 in the negative y-direction, and φ being an angle relative to the y-axis, ξ being an angle relative to the z-axis and α being an elevation angle of the capturing means, the capturing means being disposed apart from the origin of the x, y, z coordinate system by a projection distance L in the positive y-direction, the inclination is determined using the equations sinφtanξ = X − 1 + M α / 2 l tanα, and cosφtanξ = Z − 1 − M z − 1 + M ytanα / 2 l 1 + tan 2 α, whereby M=1/L, sinφtanξ is the inclination of the measurement-target surface in the x-direction and cosφtanξ is the inclination of the measurement-target surface in the y-direction.