1. A search method comprising: acquiring a search condition character string indicating a keyword as a search condition of a text and an out-of-search-condition character string indicating a keyword out of the search condition; extracting a text from a storage device storing a plurality of texts therein; sequentially matching character strings in the text with the search condition character string and the out-of-search-condition character string; registering correspondence in a storage unit if the character string in the text hits the search condition character string; changing as many correspondences registered in the storage unit as the number of the search condition character strings contained in the out-of-search-condition character string into non-correspondence if the character string in the text hits the out-of-search-condition character string; and outputting the text extracted from the storage device as a search result if correspondence remains in the storage unit.