1. A recommended information presentation apparatus, comprising: a display unit which displays text data; an extraction unit which extracts keyword candidates from the text data; a storage unit which stores semantic attributes of the keyword candidates, semantic attribute rules which contain scoring criteria for semantic attributes, descriptive phrases describing the keyword candidates, and descriptive phrase rules which contain scoring criteria for descriptive phrases; a selection unit which calculates the scores of the keyword candidates based on the semantic attribute rules and descriptive phrase rules to select a selected keyword which has a highest score among the keyword candidates; a search unit which searches an information database with the selected keyword and receives search results; and a control unit which displays the search results on the display unit as recommended information with regards to the text data.