1. A keyword input supporting apparatus comprising: a document acquisition unit which acquires a document having a plurality of components containing text data; a main component selection unit which selects a component having characters in the text data among the components as a main component; an analysis unit which analyzes the part-of-speech of the text data contained in the main component, and adds a semantic attribute to each of words of the analyzed text data; an extraction unit which extracts as a specific name a word, having one of a predetermined semantic attribute and a predetermined part of speech, from each of the words; a non-transitory storage medium which stores the specific name extracted from a document being viewed or documents viewed in the past together with a corresponding semantic attribute and selection information representing the number of times the specific name is selected as a keyword by a user; a management unit which manages the specific name stored in the storage medium in accordance with the selection information; a keyword candidate classification unit which performs classification of the specific name from the storage medium as a keyword candidate based on the semantic attribute and the selection information; and a presentation unit which presents the keyword candidate to the user, and also presents a retrieval method selection region, wherein the user selects a method of key word retrieval.