An aim is to produce a useful foreign protein in egg white in transgenic birds at levels equivalent to or higher than the expression levels achieved using an ovalbumin promoter or an actin promoter, and to reduce the great burden on birds by reducing the expression at sites other than the oviduct while achieving expression sufficient to predict the expression levels before the birds reach sexual maturity. Provided is a transgenic bird containing a nucleic acid base sequence in chromosome in a cell that forms the oviduct, the sequence containing: (a) an avian endoplasmic reticulum chaperone promoter and (b) a nucleic acid base sequence encoding a useful foreign protein, functionally linked to the promoter. Also provided is a method for producing a useful foreign protein, including recovering the useful foreign protein from the transgenic bird. Further provided is a method for producing a transgenic bird, including introducing a nucleic acid base sequence into a chromosome in a cell that forms the oviduct, the sequence containing: (a) an avian endoplasmic reticulum chaperone promoter and (b) a nucleic acid base sequence encoding a useful foreign protein, functionally linked to the promoter.
