1. A triangulation device for computing a three-dimensional position of a measurement target point using a stereo method, the triangulation device comprising: an optimum image coordinate estimation unit configured to, based on coordinates of corresponding points corresponding to the measurement target point in two images each of which including an image of the measurement target point, and intrinsic parameters and extrinsic parameters of optical instruments generating the two images, calculate correction vectors by which coordinates of the corrected corresponding points satisfy an epipolar equation composed of the intrinsic parameters and the extrinsic parameters, using a characteristic polynomial including a correction amount of coordinates of the corresponding points or a reciprocal of the correction amount as a variable, and compute coordinates of the corrected corresponding points based on calculated correction vectors; and a three-dimensional coordinate calculation unit configured to calculate three-dimensional coordinates of the measurement target point based on coordinates of the corrected corresponding points, the intrinsic parameters and the extrinsic parameters.