1. An annotation assisting apparatus assisting generation of annotation data for (zero-)anaphora resolution in a natural language text, comprising: input/output means including a display device and an input device, for receiving a user input through an interactive process with a user; reading means for reading text data to be annotated from a text archive; analyzing means for performing morphological analysis and dependency parsing of the text data read by the reading means and for outputting a sequence of morphemes having information indicating dependency structure added; predicate searching means for searching the sequence of morphemes output from the analyzing means for a predicate; object identifying means for detecting, in dependency relation associated with each of the predicates searched by the predicate searching means, that a word assumed to have a prescribed relation with the predicate is missing or replaced by a referring expression, and for identifying the position of the word as an object of an annotating process; candidate estimating means for estimating, for each position of the word identified by the object identifying means, a candidate of an expression to be inserted to the position, by using a relation between the position and surrounding sequence of morphemes and using language knowledge; candidate storage means for storing a candidate estimated by the candidate estimating means in association with the position of the word; candidate displaying means for reading, for each of the object of the annotating process, a candidate or candidates estimated by the candidate estimating means from the candidate storage means, and displaying the candidate or candidates on the display device in a manner allowing the user to select any; and interactive selection means responsive to a user instruction selecting one of the candidates displayed by the candidate display means, for adding the selected candidate as an annotation to the position.