[Problem] The present invention addresses the problem of providing a method for searching for a best promoter for reliably targeting a cancerization-causing cell in human ES/iPS cells. The present invention also addresses the problem of discovering a gene which can kill or remove a cancerization-causing cell contained in human ES/iPS cells with high efficiency. The present invention further addresses the problem of providing a method for removing an undifferentiated cell, which remains after the differentiation of human ES/iPS cells into desired cells, with high efficiency and comprehensively. [Solution] A viral vector comprising a nucleotide sequence and a recombination cassette, wherein the nucleotide sequence contains a target gene and a killing gene that are linked to each other through a sequence that enables the simultaneous expression of the two genes by one promoter, and the recombination cassette contains a promoter region, and wherein the promoter region is so linked as to enable the expression of the labeling gene and the killing gene, said viral vector particularly containing a promoter specific to an undifferentiated cell as the promoter region and others.
