A document checking apparatus includes a keyword appearance position extracting unit that extracts keywords and the appearance positions of the keywords from a target document including a confidential document; a keyword pair extracting unit that treats each keyword of the appearance positions of the extracted keywords as a target and determines whether there is another extracted keyword within a predetermined range before and after the target keyword; a feature element matrix creating unit that generates, when it is determined that there is the another keyword, combination information obtained by combining the determination target keyword and the another keyword in association with anteroposterior information of the appearance positions of the keywords; and a computing unit that determines whether the number of combination information, among the plurality of combination information of the generated target document, identical to the combination information of the confidential document is not less than a predetermined value.