A novel nucleic acid fragment which has an high activity to promote expression of a structural gene located downstream thereof, and a method for promoting expression of the structural gene located downstream thereof using the nucleic acid are disclosed. A nucleic acid fragment having the nucleotide sequence shown in SEQ ID NO:1 in the Sequence Listing, and nucleic acid fragments having the same sequence as shown in SEQ ID NO:1 except that one or more nucleotides are substituted or deleted, or one or more nucleotides are inserted therein or added thereto, which have activities to promote expression of a structural gene located downstream thereof were provided.