1. A search device comprising: a memory device including a memory area which is storing document data containing search target character strings to which delimiting characters are appended at both ends; an acquirer which acquires a keyword; a generator which generates a search character string by appending delimiting characters to both ends of the keyword acquired by the acquirer; a designator which extracts multiple partial strings from the search character string generated by the generator and designates appearance positions where those extracted partial strings appear in the search target character string of the document data; a determiner which determines a frequency with which partial strings common to the partial strings of the search character string appear with a positional relationship similar to the search character string in the search target character string, based on the designation results of the designator; an evaluator which evaluates a degree of similarity between the search target character string and the search character string based on the determination results of the determiner and a difference in character lengths of the search target character string and the search character string; and, an output device which outputs the search target character string based on the evaluation results of the evaluator.