1. An expression extraction device for extracting evaluation expressions from text having descriptions on evaluations of a specific evaluation target, each evaluation expression being an expression indicating the evaluation of the evaluation target, the expression extraction device comprising: a registered expression storage unit: registering an evaluation expression as a registered expression, associating a predetermined polarity with said registered expression, wherein a positive polarity represents a positive evaluation and a negative polarity represents a negative evaluation, said predetermined polarity being determined independent of a context or of technical terms of said evaluation expression; an expression extraction unit: extracting multiple evaluation expressions and a conjunction expression from the text, said coniunction expression, indicating a conjunctive relation between the evaluation expressions; a registered expression detection unit: receiving said multiple evaluation expressions and said conjunction expression; detecting from the received multiple evaluation expressions, an evaluation expression including the registered expression registered with the registered expression storage unit; associating the predetermined polarity of said registered expression with said evaluation expression including said registered expression; a polarity judgment unit: receiving said multiple evaluation expressions, said conjunction expression, and associated predetermined polarity; judging at least one of said multiple evaluation expressions, which is in conjunction with the evaluation expression including the registered expression by means of the conjunction expression in a form of ordinary conjunction, as being of the same polarity as the registered expression; and judging a series of evaluation expressions, which are not in conjunction with the evaluation expression including the registered expression by means of the conjunction expression in any form of the ordinary conjunction and adversative/concessive conjunction and also are not in conjunction with each other by the conjunction expression in any form of the ordinary conjunction and the adversative/concessive conjunction, as being of the same polarity as the registered expression, wherein evaluation expressions appearing in multiple positions in the text are individually judged to determine the polarities of the evaluation expression in their respective positions; a registered expression addition unit: adding the evaluation expression having the polarity judged by the polarity judgment unit to the registered expression storage unit as a newly registered expression; and an evaluation display unit for displaying an evaluation of the evaluation expression based on the polarities of the multiple evaluation expressions.
1. An expression extraction device for extracting evaluation expressions from text having descriptions on evaluations of a specific evaluation target, each evaluation expression being an expression indicating the evaluation of the evaluation target, the expression extraction device comprising: a registered expression storage unit: registering an evaluation expression as a registered expression, associating a predetermined polarity with said registered expression, wherein a positive polarity represents a positive evaluation and a negative polarity represents a negative evaluation, said predetermined polarity being determined independent of a context or of technical terms of said evaluation expression; an expression extraction unit: extracting multiple evaluation expressions and a conjunction expression from the text, said coniunction expression, indicating a conjunctive relation between the evaluation expressions; a registered expression detection unit: receiving said multiple evaluation expressions and said conjunction expression; detecting from the received multiple evaluation expressions, an evaluation expression including the registered expression registered with the registered expression storage unit; associating the predetermined polarity of said registered expression with said evaluation expression including said registered expression; a polarity judgment unit: receiving said multiple evaluation expressions, said conjunction expression, and associated predetermined polarity; judging at least one of said multiple evaluation expressions, which is in conjunction with the evaluation expression including the registered expression by means of the conjunction expression in a form of ordinary conjunction, as being of the same polarity as the registered expression; and judging a series of evaluation expressions, which are not in conjunction with the evaluation expression including the registered expression by means of the conjunction expression in any form of the ordinary conjunction and adversative/concessive conjunction and also are not in conjunction with each other by the conjunction expression in any form of the ordinary conjunction and the adversative/concessive conjunction, as being of the same polarity as the registered expression, wherein evaluation expressions appearing in multiple positions in the text are individually judged to determine the polarities of the evaluation expression in their respective positions; a registered expression addition unit: adding the evaluation expression having the polarity judged by the polarity judgment unit to the registered expression storage unit as a newly registered expression; and an evaluation display unit for displaying an evaluation of the evaluation expression based on the polarities of the multiple evaluation expressions. 15. The expression extraction device according to claim 1 , further comprising: a certainty storage unit for prestoring a certainty indicating a degree that the conjunction expression is the conjunction expression in any form of the ordinary conjunction or the adversative/concessive conjunction in terms of a type of the conjunction expression, wherein the polarity judgment unit further judges certainties of polarities of the evaluation expression in conjunction with the evaluation expression including the registered expression by means of the conjunction expression in any form of the ordinary conjunction, and of a series of the evaluation expressions, which are not in conjunction with the evaluation expression by means of the conjunction expression in any form of the ordinary conjunction and the adversative/concessive conjunction and are not in conjunction with each other by means of the conjunction expression in any form of the ordinary conjunction and the adversative/concessive conjunction, depending on the certainty of the ordinary conjunction expression, and the expression extraction device further comprises a polarity determination unit for determining a polarity of one of the evaluation expressions appearing in multiple positions in the text based on certainties of polarities in the respective positions.