This invention is intended to develop a promoter that can strongly induce marker gene expression throughout an embryo, so as to simply, efficiently, and accurately identify a transgenic insect at an early developmental stage, and to provide a gene expression vector into which such promoter has been incorporated as a transformant discrimination marker. Such exogenous gene expression vector comprises a polynucleotide comprising the nucleotide sequence as shown in SEQ ID NO: 1 as a promoter.