1. A searching device, comprising: a text memory that stores text data, the text data showing at least one character strings, the character strings including n-number of characters, n being a natural number; an input device that receives an input of a keyword, the keyword including m-number of characters, m being a natural number that satisfies m≦n; a selector that selects at least one search character from the m-number of characters included in the keyword, the search characters including a-number of characters, a being a natural number that satisfies a≦m; a search window controller that sets a search window, the search window including b-number of characters, the b-number of characters being selected from the text data, b being a natural number that satisfies b≧a; a determining unit that determines whether the search window includes the keyword on the basis of a comparison result of the characters in the search window with the search characters.