Production of efficiently producing agaro-oligosaccharide; a polypeptide having an agarase activity which is usable in, for example, efficiently extracting a substance such as a nucleic acid from an agarose gel; the amino acid sequence of the polypeptide; a gene encoding the polypeptide; a process for producing the polypeptide; a process for producing agaro-oligosaccharide; and a process for extracting a substance such as a nucleic acid from an agarose gel.