The object of the present invention is to provide a production system that is capable of high-level secretory production of a protein (and in particular, a protein with a complicated structure such as a structure with S-S bonds) in a host cell such as yeast and is suitable for industrial production with high safety that does not require explosion-proof facilities. The present invention provides a transformed yeast into which a chaperone gene has been introduced and in which the aox1 gene and/or the protease gene have been disrupted and a method for producing a protein involving the use of such transformed yeast.