1. A text mining apparatus which, when one or more of input texts as subjects of text mining is entered, outputs at least one set of a characteristic word and a characteristic measure representing a characteristic of the input text, the apparatus comprising: a characteristic word count unit that, in counting the number of each characteristic word in the input text, calculates a statistical estimation of a count result using statistical information representing a property of the input text and/or a confidence measure attached to the input text; a characteristic measure calculation unit that calculates the characteristic measure of each characteristic word using the statistical estimation of the count result of the each characteristic word, the statistical estimation being calculated by the characteristic word count unit; a language processing unit that performs language analysis of text data entered from a text input device to transform and shape the text data into units of the characteristic words; and a statistical information database that records and holds the statistical information representing a property of the input text presupposed to be entered, the characteristic word count unit counting the number of the characteristic word in the input text and acquiring an estimation of the number of times of occurrence of the characteristic word by exploiting a confidence measure provided in the input text and/or statistical information representing a property of the input text; a characteristic measure calculation unit that calculates the characteristic measure of each characteristic word from the estimation of the number of times of occurrence of the characteristic words as found by the characteristic word count unit, the characteristic word count unit finding an estimation of a count value of each characteristic word of the input text not provided with the confidence measure using the preset statistical information of the input texts stored in the statistical information database.