A transformed host cell (i) into which one or a combination of two or more of the chaperone genes (a) to (c) below have been introduced: (a) a gene comprising DNA which consists of the nucleotide sequence as shown in SEQ ID NO: 1; (b) a gene which hybridizes under stringent conditions to a DNA consisting of a nucleotide sequence complementary to DNA consisting of the nucleotide sequence as shown in SEQ ID NO: 1 and encodes a protein having activity of increasing foreign protein secretion, wherein the stringent conditions comprise a sodium concentration of 15 to 750mM, a temperature of 25°C to 70°C, a formamide concentration of 0% to 50%, the filter being washed at sodium salt concentration of 15 to 600mM and at a temperature of 50°C to 70°C after hybridization; and (c) a gene which consists of a nucleotide sequence having at least 90% homology with the nucleotide sequence as shown in SEQ ID NO: 1 and encodes a protein having activity of increasing foreign protein secretion, wherein the homology is determined using a FASTA or BLAST program, or (ii) into which one or a combination of two or more of the genes encoding the chaperone proteins (d) to (f) below have been introduced: (d) a protein which consists of the amino acid sequence as shown in SEQ ID NO: 2; (e) a protein which consists of an amino acid sequence having at least 90% homology with the amino acid sequence as shown in SEQ ID NO: 2 and has activity of increasing foreign protein secretion, wherein the homology is determined using a FASTA or BLAST program; and (f) a protein which consists of an amino acid sequence derived from the amino acid sequence as shown in SEQ ID NO: 2 by deletion, substitution, and/or addition of one to 10 amino acids and has activity of increasing foreign protein secretion. (i) into which one or a combination of two or more of the chaperone genes (a) to (c) below have been introduced: (a) a gene comprising DNA which consists of the nucleotide sequence as shown in SEQ ID NO: 1; (b) a gene which hybridizes under stringent conditions to a DNA consisting of a nucleotide sequence complementary to DNA consisting of the nucleotide sequence as shown in SEQ ID NO: 1 and encodes a protein having activity of increasing foreign protein secretion, wherein the stringent conditions comprise a sodium concentration of 15 to 750mM, a temperature of 25°C to 70°C, a formamide concentration of 0% to 50%, the filter being washed at sodium salt concentration of 15 to 600mM and at a temperature of 50°C to 70°C after hybridization; and (c) a gene which consists of a nucleotide sequence having at least 90% homology with the nucleotide sequence as shown in SEQ ID NO: 1 and encodes a protein having activity of increasing foreign protein secretion, wherein the homology is determined using a FASTA or BLAST program, or (a) a gene comprising DNA which consists of the nucleotide sequence as shown in SEQ ID NO: 1; (b) a gene which hybridizes under stringent conditions to a DNA consisting of a nucleotide sequence complementary to DNA consisting of the nucleotide sequence as shown in SEQ ID NO: 1 and encodes a protein having activity of increasing foreign protein secretion, wherein the stringent conditions comprise a sodium concentration of 15 to 750mM, a temperature of 25°C to 70°C, a formamide concentration of 0% to 50%, the filter being washed at sodium salt concentration of 15 to 600mM and at a temperature of 50°C to 70°C after hybridization; and (c) a gene which consists of a nucleotide sequence having at least 90% homology with the nucleotide sequence as shown in SEQ ID NO: 1 and encodes a protein having activity of increasing foreign protein secretion, wherein the homology is determined using a FASTA or BLAST program, or (ii) into which one or a combination of two or more of the genes encoding the chaperone proteins (d) to (f) below have been introduced: (d) a protein which consists of the amino acid sequence as shown in SEQ ID NO: 2; (e) a protein which consists of an amino acid sequence having at least 90% homology with the amino acid sequence as shown in SEQ ID NO: 2 and has activity of increasing foreign protein secretion, wherein the homology is determined using a FASTA or BLAST program; and (f) a protein which consists of an amino acid sequence derived from the amino acid sequence as shown in SEQ ID NO: 2 by deletion, substitution, and/or addition of one to 10 amino acids and has activity of increasing foreign protein secretion. (d) a protein which consists of the amino acid sequence as shown in SEQ ID NO: 2; (e) a protein which consists of an amino acid sequence having at least 90% homology with the amino acid sequence as shown in SEQ ID NO: 2 and has activity of increasing foreign protein secretion, wherein the homology is determined using a FASTA or BLAST program; and (f) a protein which consists of an amino acid sequence derived from the amino acid sequence as shown in SEQ ID NO: 2 by deletion, substitution, and/or addition of one to 10 amino acids and has activity of increasing foreign protein secretion.