1. An illumination estimation device, comprising: a target object area extraction unit which extracts an object area from a multispectral image, the object area being an area, including specular reflection, of an object; a distribution characteristics estimation unit which estimates information representing a subspace that approximates a distribution of observation values in a spectral space, as distribution characteristics, the distribution characteristics being characteristics of a spreading manner of the observation values in the object area within the spectral space; a dimension reduction unit which selects a distribution characteristic to be used from among the distribution characteristics estimated by the distribution characteristics estimation unit depending on the number of dimensions to be reduced, the number of dimensions to be reduced being determined in advance by a light environment; and an illumination estimation unit which estimates spectral characteristics of illumination based on the subspace information to be represented by the distribution characteristic selected by the dimension reduction unit.