1. A document evaluation apparatus for evaluating a document using a set of sample documents having a first feature vector consisting of a plurality of feature values and evaluation values of the documents, comprising: a data classification unit that classifies the set of sample documents, based on a missing pattern indicating a set of indices whose feature values are missing in the first feature vector; a first learning unit that uses feature values that are not missing in the first feature vector and the evaluation values to learn, for each classification, a first function for calculating a first score which is a weighted evaluation value for each classification; a feature vector generation unit that computes a feature value corresponding to each classification using the first score, and generates a second feature vector having the computed feature values; and a second learning unit that uses the second feature vector and the evaluation values to learn a second function for calculating a second score for evaluating a document targeted for evaluation.