It is an object of the present invention to provide a method for producing a low-molecular-weight antibody such as a Fab-type antibody, using yeast as a host, wherein the method is able to produce the low-molecular-weight antibody with high productivity. According to the present invention, there is provided a gene comprising a nucleotide sequence encoding an amino acid or an amino acid sequence capable of increasing the secretion amount of a Fab-type antibody at the 3′-terminus of a nucleotide sequence encoding the amino acid sequence of the Fd chain or L chain of an antibody.
