There is provided an expression method of a target foreign gene in a plant induced by a chemical substance, which comprises a step of activating with copper ions a transcription factor encoded by a foreign gene different from the target foreign gene to induce activation of transcription of the target foreign gene by a region having a promoter function contained in the target foreign gene, wherein a nucleotide sequence encoding said transcription factor is contained in a gene construct which is constructed so as to comprise a nucleotide sequence of a 5'-untranslated region of an arbitrary foreign gene downstream from the region having a promoter function contained in the target foreign gene.
