1. An annotation assisting apparatus assisting generation of annotation data for (zero-)anaphora resolution in a natural language text, comprising: a display device and an input device configured to receive a user input through an interactive process with a user; a processor configured to: read text data to be annotated from a text archive; perform morphological analysis and dependency parsing of the read text data; output a sequence of morphemes having information indicating dependency structure added; search each of the outputted sequence of morphemes for a predicate; detect, in dependency relation associated with each of the searched predicates, that a word assumed to have a prescribed relation with each of the searched predicates is missing or replaced by a referring expression; identify a position of each of the detected words as an object of an annotating process; and estimate, for each identified position of the detected word, a candidate of an expression to be inserted to the identified position, by using a relation between the identified position and surrounding sequence of morphemes and using language knowledge; a non-transitory computer readable medium storing the estimated candidates; wherein the processor is further configured to read, for each object of the annotating process, the estimated candidates from the non-transitory computer readable medium, and display the candidates on the display device in a manner allowing the user to select any of the one or more candidates; and wherein the input device is responsive to a user instruction selecting one of the displayed candidates by adding the selected candidate as an annotation to the position.