1. A question answering system which receives question statement data expressed in a natural language and outputs an answer to the question statement data from a document data group which is an answer retrieval target, the system comprising: answer type estimating means for analyzing language expressions of the question statement data entered and estimating an answer type which is a type of language expression that can be an answer to the question statement data; document retrieving means for extracting keywords from the question statement data, retrieving and extracting document data including the keywords from the document data group; answer candidate evaluation point calculating means for extracting language expressions that can be the answer from the document data as answer candidates and assigning evaluation points to the answer candidates; answer candidate evaluation point counting means for sorting and ranking, when evaluation points are counted for each answer candidate having the same language expression, evaluation points of answer candidates having the same language expression in descending order of evaluation ranking, calculating values of the evaluation points using such weighting that the value to be processed for each evaluation point diminishes in descending ranking order of evaluation points and regarding the sum total of the values as the evaluation point of the answer candidate having the same language expression; and answer outputting means for outputting answer candidates whose evaluation point counted by the answer candidate evaluation point counting means is equal to or higher than a predetermined evaluation as an answer.