1. A defect predicate expression extraction method executed by a processor device for extracting predicate expressions representing defects from text data related to use of products, the method comprising: storing in a first predicate modifying expression storage unit, as predicate modifying expressions for detecting defect expressions, at least one of predicate modifying expressions representing suddenness and predicate modifying expressions representing repeatability; detecting, in said text data, expressions matching each of the said stored predicate modifying expressions for detecting defect expressions and extracting, as a candidate for a predicate expression representing a defect, a predicate expression occurring in a neighborhood of each of said detected expressions matching each of the said stored predicate modifying expressions for detecting defect expressions in said text data; storing in a second predicate modifying expression storage unit, as predicate modifying expressions for detecting normality expressions, predicate modifying expressions representing normality; detecting, in said text data, expressions matching each of the said stored predicate modifying expressions for detecting normality expressions and extracting, as a predicate expression representing normality, a predicate expression occurring in a neighborhood of each of the said detected expressions matching each of the said stored predicate modifying expressions for detecting normality expressions in said text data; and acquiring, as said predicate expressions representing defects, predicate expressions remaining after said extracted predicate expressions are removed from a list of said predicate expressions extracted as said candidates for said predicate expressions representing defects.