The invention provides a promoter that has high expression strength and can be over-expressed in various tissues of plant, said promoter is a promoter for banana polyubiquitin (polyubiquitin) gene MhUBQ1, and has a sequence as SEQ ID No: 3. The invention provides further a gene expression cassette that contains a promoter comprising a DNA sequence as SEQ ID No: 3, and a polynucleotide having a open reading frame (ORF) linked to the 3′ terminal of said promoter, wherein said promoter can activate the transcription of said polynucleotide in a organism containing said gene expression cassette. The invention provides further a gene expression vector that contains a promoter having a DNA sequence as SEQ ID No: 3. Also, the invention provides a process for producing a transgenic plant or part of organ, tissue or cell thereof containing the above-described gene expression cassette.