1. A data processing method based on collective document data containing sentences by different writers for generating a candidate synonym for an object word used in the document data, the data processing method comprising the steps of: inputting the object word as a concept for candidate synonyms; generating at least one piece of partial data of the collective document data for a writer, the partial data containing only the sentences by the writer; extracting words contained in the collective document data based on the object word by calculating degrees of relatedness between the extracted words and the object word, and generating a first set of candidate synonyms, which has as elements for the first set, a predetermined number of the extracted words ranked highest in descending order of the degree of relatedness; extracting words contained in the partial data based on the object word by calculating degrees of relatedness between the extracted words in the partial data and the object word, and generating a second set of candidate synonyms for the writer, which has as elements for the second set, a predetermined number of the extracted words ranked highest in descending order of the degree of relatedness; evaluating, among the words contained in the first set of candidate synonyms, the words of the first set, which are matched with the words ranked in places equal to or higher than a threshold value place in any of the second sets of candidate synonyms, are evaluated to be absolute, wherein said absolute, is a definitive candidate synonym; evaluating, among the words contained in the first set of candidate synonyms except the words evaluated to be absolute, the words of the first set, which are matched with the words ranked in places lower than the threshold value place in any of the second sets of candidate synonyms, are evaluated to be negative, wherein said negative is not a definitive candidate synonym; and generating the candidate synonyms for the object word from the words of the first set of candidate synonyms by excluding the words evaluated to be negative, wherein the calculation of the degrees of relatedness is realized by the steps of: extracting all words of a first word class and all words of a second word class from the document data or the partial data, the words of the second word class having modification relations with the words of the first word class; generating a matrix using all the extracted words of the first word class and all the extracted words of the second class as indices of rows or columns thereof, the matrix having a size of the number of the words of the first word class by the number of the words of the second word class; substituting a frequency of the modification relation between the word of the first word class and the word of the second word class with elements for the matrix and indexing each element of the elements into the matrix; extracting said each element of the elements of the row or column having the word of the first word class matching the object word from the matrix generated based on the document data to set the row or column as an object word vector; extracting each element of the elements of an arbitrary row or an arbitrary column from the matrix generated based on the document data or the partial data; setting the row or column as a vector of the word of the first word class indicated by the row or column; and calculating a degree of relatedness of the word of the first word class with the object word by taking a scalar product of the vector of the word of the first word class and the object word vector.