2. The requirement acquisition system according to claim 1 , wherein the character string extraction section is configured to calculate a distance between each of the plurality of character strings and the document, and extract a character string among the plurality of character strings the distance thereof is minimum as the candidate character string.
3. The requirement acquisition system according to claim 2 , wherein the character string extraction section is configured to calculate the distance between each of the plurality of character strings and the document based on an approximation calculation method of a Kolmogorov complexity.