The present invention relates to a method for producing a heterologous protein secreted out of a plant cell comprising introducing into a plant cell genome a DNA encoding an amino acid sequence that comprises a glycinin signal sequence for endoplasmic reticulum transport and an amino acid sequence of a heterologous protein, wherein the signal sequence is directly fused to the amino acid sequence of the heterologous protein or one or two amino acids are inserted between the signal sequence and the amino acid sequence of the heterologous protein and expressing the DNA.
