1. A searching device for searching information, comprising: a history storing unit of a processor, storing information of a search target obtained by a search and a search date in a storage unit; a relevancy storing unit storing in said storage unit a previous searching keyword including a plurality of date-related words as well as said search target and an attribute of the search target in association with one another; a change unit changing the previous searching keyword stored in said storage unit, based on the search date stored in said storage unit and a date output from a clock unit; a reception unit receiving a previous searching keyword and said search target or the attribute that are entered by voice; an extraction unit extracting a search target corresponding to the previous searching keyword and the search target or attribute received by said reception unit, by referring to the previous searching keyword that is obtained after changing by said change unit, the search target and the attribute that are stored in said storage; and a search date output unit outputting a search date for each search target stored in said storage unit, when a plurality of search targets are extracted by said extraction unit.