1. An information displaying apparatus comprising: a main dictionary storing section to store main dictionary information in which words to be studied are associated with respective explanation information; a sub-dictionary storing section to store sub-dictionary information in which words to be studied are associated with respective explanation information; a displaying section including a retrieval character input area, a word list displaying area to display word lists of the words to be studied respectively retrieved from the main dictionary information and the sub-dictionary information regarding a retrieval character, and an explanation information displaying area to display respective explanation information of the main dictionary information and the sub-dictionary information regarding words specified from the respective word lists displayed in the word list displaying area; a main word changing section to change a main dictionary specified word by specification of one of the words from the main dictionary word list displayed in the word list displaying area, the specification being made according to a user operation; a sub-dictionary word update displaying section to retrieve the changed main dictionary specified word as a new retrieval character from the sub-dictionary information and to update display of the sub-dictionary word list in the word list displaying area; a sub-word respecifying section to specify a first word in the updated display of the sub-dictionary word list as a sub-dictionary specified word, wherein the first word is the same as the changed main dictionary specified word, and is listed first in the sub-dictionary word list by skipping each word stored only in the sub-dictionary information in the sub-dictionary word list between the word in the sub-dictionary word list corresponding to the main dictionary specified word before the change and the word in the sub-dictionary word list corresponding the main dictionary specified word after the change; and an explanation information update displaying section to update display of the explanation information to display explanation information of the changed main dictionary specified word and explanation information of the sub-dictionary specified word, which is the same as the changed main dictionary specified word and is listed first in the sub-dictionary word list, in the explanation information displaying area.