1. A retrieving apparatus comprising: a plurality of first storing units including a content-information storing unit that stores therein electronic program guide data concerning a broadcasted content and a content-material storing unit that stores therein additional information including a recorded content and at least a part of the electronic program guide data for the recorded content; a second storing unit that stores a word dictionary in which a plurality of registered words, a reading of each of the registered words, a family attribute representing a relation between a formal name and an alias of the formal name among the registered words, and a presence attribute representing from which of the content-information storing unit and the content-material storing unit each of the registered words is extracted are associated; an external communication unit that acquires related information including a plurality of words, a reading of each of the words, and a family attribute representing a relation between formal name and an alias of the formal name among the words, from other word dictionary in which a relation between each word and the alias of the each word is updated at a predetermined time interval; an extracting unit that extracts a word that is in a family relation with a registered word in the word dictionary and a reading of the word, from the related information; a registering unit that registers, in the word dictionary, the word extracted from the electronic program guide data and the additional information, in association with the presence attribute, and that registers the word and the reading of the word extracted by the extracting unit in the word dictionary in association with a family attribute representing the family relation with the registered word; a speech input unit that receives an input of a speech signal; a speech recognizing unit that recognizes a character string corresponding to the speech signal as a keyword; a retrieval-candidate expanding unit that retrieves a word coinciding with the keyword and a word familiar with the word from the word dictionary as a retrieval candidate word; a retrieval-word selecting unit that receives a selection designation that designates any of words included in the retrieval candidate words as a retrieval word; a retrieval-word expanding unit that sets the retrieval word and a word familiar with the retrieval word as expanded retrieval words, based on the word dictionary; and a retrieving unit that retrieves a content related to any of words included in the expanded retrieval words one of the content-information storing unit and the content-material storing unit represented by the presence attribute associated with the word.